Turrets have Durability now (somehow it got deleted earlier). 

Summary of game:

Turret 5 is extremely cheap and powerful but only fire 10 shots
Turret 4 has a lot of piercing to clear the crowd of the weak guys
protecting the boss
Turret3 is the most powerful
Turret 2 has greatest slowing
Turret 1 is cheap and durable, but slow