Read reviews for the B507 by Stearns as submitted by your fellow paddlers. All of the reviews are created and written by paddlers like you, so be sure to submit your own review and be part of the community!
If you haven't run much whitewater, I would suggest starting out with class II or less, until you understand how to brace and eddy turn. It's not as forgiving as the tradition "ducky" design, and the potential to flip is greater. Still, it's much more stable than a hard boat, and you can do alot of the same play moves.
My only complaints are that the bottom material, which appears to be about 1100 denier pvc fabric, could be susceptible to wear over time, but that's speculation. It's overall a very tough little boat. Another key is to inflate it in the shade to avoid loss of air pressure when hitting the cold water. If you're in class III or above, you'll want as much rigidness as possible. That said, it's a quite rigid boat, kudos to Stearns for their design here.
For one since it doesn't have a skeg, it not good for alot of flatwater paddle due to the fact that it has no tracking and is hard to keep straight. Probably with a really, really good stroke it could be done, but throw in wind and current and it gets a little squirrly. The other thing that is my biggest complaint is that it seems like such a cramped space. I'm about 5'8-5'9 and weigh about 150 give or take and I felt very cramped. It didn't have alot of leg room. I got used to it, but I always feel cramped.
Other than that I love the boat and would buy another one if the need was there!
However, if you need a kayak that you can stuff in a dufflebag, and toss on a plane to go someplace, the Stearns is a good choice. Well made, and the price is right. (I got mine on the internet for $309)
I view my Stearns as a specialty item, for travel purposes, and it fits that bill very well. Price and quality are its two most attractive features. I am looking forward to playing with it in some surf in the near future, and will re-rate it afterwards.