Disposition, tameness, noise level, temperament, any specific requirements to the species.
They tend to be very placid and do get bullied easily. I do however have one hen that will dish it out just as bad if anyone annoys her.
Tameness they aren't really a cage bird they are an aviary species, I find mine never settled in a cage and they aren't 'tame' in the way a budgie is. Mine will come over to me and climb all over me in the aviary but only on their terms. They will not step up etc. I handreared two of the chicks myself. Once they wean they go through a very flighty stage if being spooked by everything regardless of being handreared.
Noise wise they tend to be pretty quiet. They are active dawn and dusk more so than during the day and this tends to be when they are noisiest. One of my boys has a big set of lungs on him and can get really loud lol.
They are a grass parakeet and as such do spend a LOT of time in the floor and are far more susceptible to bacterial infections. They prefer more greenery in their diet than budgies tend to. They also do not fly like other species. Whereas budgies will tend to fly directly to where they are going Bourkes will 'flutter' and require a lot more space than budgies. Another reason they are better suited to aviaries rather than cages. You can not house them with budgies in a cage, it can work in an aviary if you have enough space and watch your birds carefully and be prepared to separate if needed.
I had a few in the past and loved them. As stated above, they have a greater need for space than budgies and seemed a bit flightier - though not in the spooky sense, mine just liked to be able to fly about rather than climb. That probably makes them more of a large cage bird.
They were not handled at all, but would land next to my shoulder to see what I was doing, and on me if I was holding anything that may have been a nestbox, scurry down my arm and investigate it! My unhandled budgies were definitely not as naturally tame as the bourkes.
They make a lovely soft twittering sound, no screeches or loud chirping. When they fly their wings make a quiet whistling sound which I also really liked. Mine were also much more gentle than budgies and I would have liked to have tried handraising as I think they are just adorable and I wanted one inside wtih me....
They come in a few of colours (I like the pinks as I couldn't get pink in budgies, so they rounded out the rainbow in my aviary...) and are one of my favourite birds.