In my experience, teslas can work in a small group whereas turrets cant. Ex. 1 tesla blocking a minor chokepoint.
The major advantage of the tesla over the turret, is that they do not need to turn, and they do do more damage than turret, if the turrets are forced to turn.
example, when a decent goon attacks 2 turrets, how does he approach?
He ll probably prounce + chomp , tank 1 turret , leaving him around 100hp , then circle the other turret ( force it to turn ) without taking anymore serious damage.
However, like i stated above, once turrets gets in the group of threes, they are starting to become more effective than teslas, even a good goon needs to think twice before trying to take down 3 turrets at once.
But, teslas do have another advantage over the turrets, and that is against maraduers, for the obious reasons that mara bounces alot and turrets suck at aiming.
In the hands of a good builder, teslas are rarely needed, the turrets alone will do its job , kinda like aliens' hive, tubes + trappers are superior most of the time.