I have been using these face masks on and off for a while now and I think they are really good. Despite being 27 I suffer a lot with spot breakouts and scarring, but these masks have definitely helped. I apply them after exfoliating, as a little tip I learnt from my beauty therapist is that it's best to apply masks to new, freshly exfoliated skin. I am always a little unclear as to whether the best way to use them is to apply them to a damp face (after rinsing from the exfoliation stage) or a dry one, as the instructions on the back simply state `Cleanse, Apply, Relax, Rinse', but I usually just apply to a damp face and I find that works fine.
I normally use one sachet every Sunday night (I daresay you could get two uses out of one sachet but I like to apply it nice & thick), leave for 15-20 minutes before rinsing, and usually by Tuesday/Wednesday any spots I have start drying up/healing. I'd like to think they help stop new breakouts from reaching the surface, too. I'd definitely recommend using one of these masks at least once a week for a nice deep cleanse, especially if you have spot prone skin :-).