I too only use this, when and if I think the plant needs the extra boost.
Also, I only use it once.. during the veg cycle.
I've never used it during flowering.. and don't plan to do so either.
I've also never heard of anyone ever using ST during flowering.. and I'm not sure if it would have negative or positive effects on the plant.. while its flowering. So, until someone else tries it.. and shares the results.. on using ST on a flowering plant.. I won't use it during flowering. Not about to mess my plants up.. I got too much love for my babies to try that.. without knowing or having an idea of what the effects would be on the plant.
Anyhow, I can tell a slight difference in size... when I compare a plant that I've given ST to; versus a plant that hasn't gotten a dose of ST at all.
Leafs seem bigger.. and the main stem seems to be bigger and more robust. Just more healthy looking overall... that's about it.
But hey, that's nothing to sneeze at.
anyhow, that's my 2cents worth.. about using ST.
so yeah, IMO, Superthrive does work.
peace.