I'm looking into getting a knee scooter/rollabout, but I've heard a lot of bad things about their usability outside--that you hit a crack in the sidewalk or a piece of gravel and the thing will throw you. I've done a ton of looking on the internet, but I haven't had much luck finding out if one is better than another.

Who uses or has used one and could tell me your experiences with them?

I have a rollabout, wish I had of gotten the one with the bigger wheels. They are out of Felton, DE I believe. my insurance company paid for it so I am not sure of the cost.
yes I hit some gravel and it throw me, but It was alot and I was going fast.

Wish I could help but I have a walker (with 4 wheels) not the kind you kneel on. I mean...I kneel on the seat of mine often when I am standing and sometimes if I need to just scoot a very short distance...but it's not made for that. I know in doing the research for mine it was critical to get the larger wheels and they are better on uneven surfaces. It also helped a lot to read reviews on websites (amazon.com had a lot that were good for me). You'll read about lots of things you might never have thought of yourself and people are usually brutally honest about the pros and cons in those reviews.