What are the best? I know nothing about them. Living in VT they seem like the way to go.
Are they reliable? Are they enjoyable?
Depends how you define "enjoyable". Like maybe, the sheer pleasure of reaching the cool-down stage? I have a selection of Spinervals from Coach Troy and his gang of self-abusers. Some of his dvd's are quite hard and I find myself gearing down from his recommendations. They do make a difference. Depending on your fitness level, try one of his easier programs first before buying an armful.