the sst 40.5 and tnt are both awesome decks. I love them both. But they are very different. the concave is more mellow on the sst and the sst is heavier and spins slow. also the pop isant instant like the TNT because of the flex, kind of lkike a delay.
The TNT makes everything instant and percise. It reacts as fast as you do. It also spins fast and smooth. The concave also locks your feet in on wake to wake tricks which prevents your feet from moving off the board while in the air like i felt with the sst.
Either deck is great though, but those are the differences i noticed.