Firstly - The Turret is reclaimable by bushwhacker in this animation phase. While it is hard to pull off (hitboxes are often wonky). It gives Bushwhacker the opportunity to shorten the cooldown for his next turret considerably. Which is a heaven sent if it gets shut down while you were setting it up.
Secondly - The turret is good. But takes some learning. You have to get a feel for his maximum range (close to near midrange I say). And he isn’t strong on his own, outside of situations where people ignore them.
Some good uses for the turret.
Flanking warning. Place the turret to cover one way. Guard the other one yourself you will hear him firing and get hit indicators as soon as someone comes that way.
C4 protection. Both as a shortime damagesponge while placing. And as a guard. Place him out of sight and aiming at the objective. He eats lemming rushing engineers for breakfast.
Crossfire/Decoy. Set him somewhere stand somewhere else covering the same position enemies have to choose you or him (also adds up to your own DPS).
General pointers. When your turret starts firing and can’t produce a kill message in an instant, you have to assist him immidently or he is lost. Against good players the turret is just a 2 seconds slowdown at best.
Allways attack with your turret never place a turret and then hide behind a corner hoping he does the work for you. The turret gets destroyed, the damage he did gets healed and you accomplished nothing.
This goes especially for non bushwhacker players. The turret is 0.5 of a additional Merc in combat that adds a nice chunk of damage to a fight. If you wait till he is gone you are wasting his potential.