As a trio, they're great, absolutely.
The three of them actually have a lot of synergy, design wise, and also work well with their last-gen counterparts as defensive (and in 2/3 cases, offensive) typings and set ups. If bulletproof fucked with arrow moves from Decidueye then Chestnaught and Decidueye both would check each other pretty darn well.
They also stick in a general, though slightly messed with, thematic that Kalos also brought along in the form of the Fighter/Mage/Thief combo as well.
However, singularly their designs are a little too devicive. Primarina uses a design theme that works really well on paper (as sea lions were commonly mistaken for mermaids), but really shouldn't be used as one of the major choices of the game.
People aren't huge fans of Inciniroar if only because of his huge hands, but they did the thematics well and I'm more than willing to give the big lug a shot.
Decidueye works the best out of the three as a standalone design because he has a much more easily determined theme right off the bat, especially with the whole thing of sneaky archers/assassins being really cool to the eyes of people in general, despite Decidueye being a big dork in description.
While they could have given us a little better explanation for the type change Its because he doesn't fly and is a nimble and dexterous ambush attacker, good at avoiding more conventional attacks, but shit-all at taking ambushes himself. everything else about Decidueye is incredibly sound, especially compared to the other two.
