I've never tried them but I also don't use airstones on any of my tanks either. Bettas can breathe from the air due to the slow moving, warm water of their natural habitat, so it isn't necessary but the biggest reason for me is the noise factor because my tanks are in my room.
The tablets sound like a gimmick. Airstones will send your betta into a frenzy. They're too bubbly and stressful. What you want is a REALLY dinky air pump (should cost you 15 bucks max), a gang valve (maybe 3?) and a sponge filter (a cheap one. You can even make your own). Sponge filters are as good as you can get for bettas, and also really cheap. Its sponge or bust, man.