They're even cheaper if bought overseas. There's a reason why experienced airsofters rave about the TM piston, it's value is unmatched. It's very strong; more than strong enough to pull 410+ fps easily, despite being a "stock" piston for aegs that shoot 250 fps. Unlike other more expensive pistons, it'll generally and gradually wear down as opposed to catastrophically failing. Only thing it can't really do is pull a 400 fps and shoot 30+ RPS. The first piston tooth will rip right out despite everything I try. Maybe I'm just expecting too much from such an inexpensive piston?
The only real issue is that the piston comes with the stock TM piston head, which can be a bitch to remove if you're unlucky.