There are no 6 or 8 inch "stealth wheels". Those products simply don't exist.
There is the 6in. "2008 FIRST Wheel" and the 8in. "2010 8" FIRST Wheel" (
https://www.andymark.com/product-p/am-0144.htm and
https://www.andymark.com/product-p/am-0420.htm respectively)
With that out of the way our team did use the hex bore stealth wheel a bit in testing and found that they were not very grippy. They were adequately strong to support an FRC robot and very light and cheap but otherwise not worth it. We found they didn't mark up the tile in our school much so that is pretty great for a demo bot. They also didn't wear down very much but then again we didn't do much testing. They're pretty hard so we'd expect them to last a while.
The new vex hex bore colson wheels look like a pretty great replacement. At $9.99 the Colson Performa (4" x 0.875", 1/2" Hex bore) wheels would drop in pretty much anywhere the stealth wheels would and will provide much more traction (colsons are great) and are also nonmarking and last a long time, but are heavier and more expensive. (
http://www.vexrobotics.com/vexpro/mo...nperforma.html)