I used to take them. The Sustain is basically a calcium/D/K vitamin. The Stim is that, plus some other supplements that he says have been shown to promote bone health. He describes them in his book.

There is nothing dangerous, and he doesn't use megadoses of anything. I just decided I'd rather do calcium/K/D on my own, especially getting calcium from food as much as possible. Also, it's cheaper!

Another reason is that a pill may contain something that you're already getting from food. It's good to remember that the pill is not the only source.