Toxic and harmful don't mean the same thing. Nails aren't toxic, but you shouldn't eat them, or pound them into yourself. Dust isn't toxic but you shouldn't breath it in.
The stuff goes airborne easily and I'd avoid breathing too much in. But mainly people complain about the mess. The stupid bottles open too easily, and then coat everything in that pocket or bag, and doesn't wash off very well.
Personally I prefer paste floatants for anything with hackle, which is mostly what I use. CDC and soft hackles are a different matter, though. It has its uses.