I've been using them and a tub goes really far as it's quite sweet so you only need a little. Haven't had any problems with ketosis
They mix well in plain water, but for sparkling water you need to mix a little in plain water first (almost to make a kind of paste) and then add the fizz.
Hmmm, I don't find the peach weak at all, I actually find a little goes a long way. Maybe the batches are different (not beyond the realms of possibility with exante) or maybe our tastes just vary...