For clusters it is. Why? Because with clusters, you will have to unrack the weight and bring it into the starting position which is hard by itself and will take some energy which will not contribute to your gains.
Bottoms up starts take that away.
And they also have a cool effect on the nervous system; you start from the stretch position... but normally when you start from there the stretch reflex kicks in, but it doesn't anymore.
What happens is that to compensate for this the nervous system will overshoot its activation signal. Then you move on to a regular exercises and the CNS is still in overshoot mode and thus you are actually much stronger.
This morning we trained Dr. Tim Hall... this guy had never in his live lifted more than 250lbs on the bench... and he actually stopped bench pressing due to shoulder issues.
This morning he was actually able to lift 315lbs for 3 reps, pain-free, with his first try at this program.