i have started to use it Dave, i put two and a bit cap fulls in roughly 450 of water and found it frothed a lot, i used about 200 lts of the water and then filled up but didn't add any more GG4 into the tank, so in effect its gone from roughly 10 ml to 5 ml (two and a bit cap fulls is about 10 ml) and i found it a lot better so i think i will keep it at about 1ml per 100 lts or so.
Personally i find it does glide a bit better, seems to clean the frames a bit better but not had a chance to see the glass when dry, so early days yet but have no negatives about it
Bob