So I bought them used off a guy, and while they have the probax labels on them, the bladders were removed. Not that that matters though, as the location for the pump tube would be almost impossible to route to a usable position... at least in mine.
As for comfort, I like them a lot, they have a decent amount of foam padding in them, and make for a nice ride. My last 2 rides were 90miles each and there wasn't any real issue of comfort related to the seat. I think they would be pretty good for track. I think they are will be good for track, they are solid, come from another proven track car, and are setup for 4 point harness and can easily be converted for 6. Mine already came this way. I used this setup for the exige belts to create solid sub belt mount point. http://www.sector111.com/parts/track/interior/sys.cfm