I haven't reached the hormonal age with my female IRN yet so I might have to update this later, but I'll post what I know so far. I'm including some info I've heard from other IRN owners as well, to try to give a more complete picture of what you might experience.
The good:
Extremely intelligent, and a lot of fun! My IRN is soooo stable and what I would personally consider very easy compared to my other birds, who act more like needy toddlers haha. She has moods, but she's so freaking predictable, and easy to read if you pay attention. She will eat almost anything, learns what I'm requesting of her so quickly, and is easy to please just by putting her in her favorite area, talking to her, or giving her a treat or new chew toy. She will do the cutest things like sit on my monitor and chase my mouse cursor with her beak. It literally took me like 3 seconds to flight train her...I held up a perch and held up a treat behind it, and she flew to it lol. Now every evening, I just take out a treat bag and walk past while calling her the fly to my hand, while I'm doing other things. Almost zero effort training sessions nowadays, and so much fun. It's so cute when they get excited and their little eyes pin too
My IRN doesn't talk yet, but if you want to hear how incredibly cute their little voices are, just search youtube for Bowie the IRN or something. (Both the males and females are capable of speaking and very good talkers apparently, although not all of them will speak obviously.) In terms of noise level, my IRN is by far my quietest bird. She made a semi-loud noise a couple of times, and I told her "no" and covered her cage for just like 10 seconds (since leaving the room wasn't a good option at the time). When she makes a softer sound, I go to her right away and praise her. She's really smart, so she learned very quickly to make softer sounds to get my attention. Other people say their IRNs are loud though, so I might've just been lucky so far. I haven't really tried to pet her yet, but after practicing a bit if I would say "boop boop" she'd let me boop her beak and pet her beak. She has let me pet the front corner of her head above her eye next to her beak too lol.
The bad:
Something to consider is that two female IRNs don't mix, and male+female pairs might not get along, so if you want two then you might consider getting male IRN. Male IRN also seem to get along better with other birds from what I've heard and seen on youtube, whereas my female IRN will lunge if my other birds get too close (even though she likes sitting near them). Those are the only things I would personally worry about when selecting a gender.
I think IRNs get a bad rep sometimes because they think a bit differently than most other parrots, and require a slightly modified approach. They are kind of like a large bird in a small body, but they can still end up puzzling experienced large bird owners. Some people think IRNs are trying to assert dominance or "test" them with aggression, and they respond by asserting dominance back or ignoring the behavior, neither of which are very helpful. If an IRN is aggressive or tries to bite, it is almost always in my experience because of extreme fear, protection of territory, or being mischievous (usually means the bird is bored lol). IRNs really just require maybe ten minutes per day of training, nothing difficult, just working on step up, targeting, or flights to build trust and confidence at first. I've met people who try to force IRNs onto hands thinking that they are biting just to be difficult/bratty, but IRNs can be really terrified of standing on hands and fingers. You might not experience this problem at all if you go with a really good breeder, but if you buy one from a bird store that grabs them out of their cage and forces step-up, it will probably take a few weeks to work through this like it did with my IRN. They can be very fearful, and my IRN's fear-response is often what I call "remember the alamo" style, where she is like, "you can eat me but I'll go down fighting!" haha. Too many people assume this is because they're mean birds, whereas usually it's just fear. You want to work on gaining trust, not "forcing them to behave" or something like that. Training methods you can 'get away with' for other species, do not work with IRNs. On the other hand, a lot of people are given this terrible advice to just "ignore" the bird's biting and negative behavior which leads them to problems. You really should just do a bit of training each day with positive reinforcement to show the bird what behavior you value, not ignore and let it run amuck like some people suggest. I think this advice came from a desire to avoid rewarding the bird's biting behavior (i.e. don't scream or the bird might think that's fun), but it got warped over time.
There are also other good ways to avoid some potential biting. My IRN is cage aggressive, and I just use a perch to get her out of the cage. Easy! I didn't try to use my hands with her at all the first week that I had her so that she would feel comfortable, but it still only took about 3 weeks to get her consistently stepping up, understanding what "no" means, and flying to me (she's so smart!!! my smartest bird). It was so much easier to train her than my pionus, but the reason I put it in "bad" is because people who are new to bird training can end up in difficult situations and get overwhelmed. I would say my IRN learns much faster than my other birds, but requires training the most. So make sure you either have bird experience or have studied bird training (I recommend either the free Morgan the Macaw youtube series or paid Family Friendly Parrot training course, since I learned a lot from those). A lot of people say IRNs are difficult to train, but what I think they mean is you need to basically know what you're doing. It might be easy to get an IRN to fly to you, but harder to figure out how to convince her that her vet carrier isn't too scary and that she shouldn't play with other bird's tails lol. Some patience is needed. They are really sweet, smart birds underneath it all, though. And also like I mentioned, if you get the bird from a wonderful breeder who socializes them carefully, you might have nothing but smooth sailing. Some people say that their IRN has never even tried to bite and is very affectionate from day one.
The ugly:
A girl posted on avian avenue recently that she had an IRN who was going through a phase where he was continually landing on her and giving a lot of bloody bites which sounds terrifying, but she was apparently able to resolve it thank goodness by adding some foraging toys and doing target training. This was a male IRN, and I've heard a few other cases where male IRN can get like this. I don't know if it's specific to males or not. My understanding is that training resolves it or prevents it from happening, although I don't have direct experience with this extreme of a circumstance. It becomes "ugly" when people trust bird sellers to inform them and aren't properly educated on what to do, which is why I wanted to write this to make sure that anyone considering an IRN will take it into account. (That particular girl seemed to have only been given advice to "ignore" and accept the bird's behavior until it passed, which was unfair to her and inadequate advice from where she purchased the bird. Luckily she got better advice from avian avenue people, and she was brave and kind enough to work through it successfully and not consider rehoming the IRN.)
Don't let this make you afraid to get an IRN, though! My IRN gave me a bloody bite at the bird store and bit off a flap of skin when the store owner encouraged me to hold her, but she's never given me another actual bite or drawn blood since then (only some "warnings"). I have a nice communication system set up with her since she's so smart. For example if she is willing to step up on my hand, she'll wiggle her foot in the air (which is so cute). Otherwise, if I *really* need her to step up and she's not offering, then I'll use a perch and let her bite that
I think as long as you are careful where you put your hands and you make sure to do daily training, and/or buy a well adjusted bird from a great breeder, you will avoid most of the potential problems. I haven't had any ugly with my IRN
If you are intimidated by IRN problems that some people experience, I've heard of people taking in rehomed birds that were already trained and they didn't have any issues. (Just keep in mind there's often a reason those birds are being rehomed, i.e. noise level, but I've heard a few really positive stories.) Or if you don't want to try that, you might consider a mustache parakeet. Everyone seems to say that mustache parakeets are less likely to bite or scream, and more likely to talk, than IRNs.
Overall, I'm so happy I have my IRN and she is wonderful. If you like the idea of large birds and you think you're ready for a small challenge, IRNs can be kind of like a big bird in a small package. Despite the potential problems, I highly recommend them as a pet.