Which algae is this good for ? Is there any that you would consider this a waste of effort on ?
It appears to be good for anything except hard spot algae. With those, any chemical treatment only kills the outer layer; which, since it takes a few days for the killed portion to flake away, effectively shields the remainder from exposure. So an effective treatment only shrinks a spot.
I've completely removed heavy spot algae from both an anubia leaf and a resin ornament, mostly just to see if it could be done. It took somewhere in the range of seven H2O2 spot treatments, over three weeks, for complete removal. Definitely a waste of effort!