Andy Mark Traction Wheels?

[Deepthought2491]

Alright, our team is hoping for a robot with as much grip as possible. As a rookie team, we don't have any huge mechanical add-ons to our robot, so our goal is to make the best, most useful basic chassis we can. We're hoping to use really grippy wheels, and we found the Andy Mark traction Wheels, which look good, but I have a couple questions.
1) Has anybody used these? If so, read on.
2) Will they fit with the sprockets that come in the kit of parts, or would we have to buy new sprockets and/or hubs?
3) Are they any good in competition? Are there any noticable issues with using them?
4) Are they worth the $50 per wheel, or is the amount of performance gained (if any) not worth the money?

Thank you very much in advance,
Team Deep Thought