I don't know what health effects you're worried about. I haven't heard of any serious side effects when used properly, except the isobutyl compounds, which are apparently carcinogenic and banned in Europe now, anyway. Of course, mixing with Viagra or any other vasodilator is dangerous.
As for the sensation, it's difficult to describe exactly. It feels to me a bit like being drunk on alcohol, except it only lasts a couple minutes. While having sex, it definitely does change the experience. I can't really explain how, though. It's not something I use every time, but it definitely does feel nice from time to time.