The amount of people arriving here this year looking for ways to refill a bac pac is somewhat odd. Apparently word is getting out how overpriced it is. Unfortunately that's true of all Frog items, the chlorine tablets aren't the only one. Not to mention much of it is going to cause other issues (staining, overstabilization, etc) that will be even more expensive to fix. On top of it providing an inferior swimming experience to pools managed to TFPC.
From a former Frog user, I welcome you to TFP! I hope you will check out the link Marty posted above, as well as the rest of Pool School. You'll find some of the reasons I am a former Frog user there.