Its actually a russian stock that was part of the kit (its a bulgarian rifle that was demilled, but they used some russian parts like stocks and trunnions). I'm pretty happy with it. It has a nice feel to it, very close to a normal buttstock.
ACE is probably a better way to go for a rifle that you already have. A new triangle stock like mine, with trunnion and hardware is probably $130+, and it requires a LOT of receiver work to add it.
If you're having a kit built up, its a nice option, but still pricey. When I had mine built it was $150 total difference. With todays prices it would a decent amount more, and I dont think I'd bother. Its almost always open anyway, since it cant fold when the kobra is mounted.