Since this seems to be one of the more recent threads about this product, I wanted to note that I had a bit of an epiphany recently in terms of optimizing its effectiveness. This may be very obvious to others, and may have been discussed elsewhere, but it had never occurred to me until my most recent brew.
I was struggling some with precision in fermentation temperatures--the bag does a pretty good job of keeping the temp constant during or after fermentation, but I was having trouble getting the exact temperatures that I wanted (as measured through a thermowell). I felt like I was doing a lot of mixing and matching of frozen bottle sizes to get it exactly where i wanted it, and I had a couple of underattenuated batches because the beer temp would drop rapidly once active fermentation was over, leading to premature flocculation.
I happen to have a temp controller and brew belt that I've used for making saisons, and I realized I could hook both of those up to my fermenter, and pack the cooler full of frozen water bottles to achieve a temperature lower than my target ferm temp., and set the controller and heater for my desired temperature. I've been keeping my current brew at an exact 65 during fermentation using this method.
This obviously wouldn't really work if you're fermenting in a 90 degree room, but the bag should give you enough cooling power for it to work at most normal household temperatures.
