It locks the turret to only being able to rotate 90 degrees in front of the tank (so it can't shoot behind itself) and reduces essentially everything people like about the KT damage, scatter, AoE, ect in return for RoF.
It wouldn't make any sense on the StuG III for obvious reasons.
It reduces nothing but turret rotation for sight and "tracking". Damage is same, AoE and scatter seemingly same as squads seem to die as normal to it, so i noticed zero difference. It wouldnt be worth mentioning if there was one anyway. Perhaps its vet 2 buffs doing their thing or something...
RoF isnt different either. Testing this, i realized that with vet, the MG on the KT allows it to suppress squads. Though KT needs to kill 3 armies by itself in order to get that much xp... No wonder i didnt know it did that.
And at vet 4 with spearhead activated, KT has ele/ISU telescopic sight. Fat chance getting a Kt that far, though.