Check out this link, it's a good place to start.
Every plant hormone is beneficial if used at the right time, under the right circumstances.
Powerbloom sounds like a chemical pincher, which I find unnecessary. I prefer to actually pinch the tips of the newest leaves, mostly because it's free. Lol
The two ethelyne products you mentioned are intriguing though, as I have not heard of adding ethylene to increase fem ratios besides the Banana peel / Apple peel theories.
I have a hard time believing that adding ethylene will encourage the plants to start producing their own ethylene though. It would seem to me that when you stop spraying, the levels would go back to normal. Gunna have to do some searching on Google Scholar.
Addendum: Quote from sensaspray; ”However, when sprayed at the right time, Sensa-Spray™ plant hormone will exert pressure on your male plants to produce female flowers. ...
Also, you will undoubtedly have some bisexual plants (both male and female flowers on the same plant), but who cares – you win both ways!"