the yanks swear by them.................. I dont rate them.
They are good at keeping batteries topped up with daily driving. They WONT charge from flat and they wont charge a tick over..... So you will always have fully charged batts when you are on the road but if you flatten them at a show [which is where you need topped up batts] they are no use at all................. A decent set of batts will last a couple of weeks between charges for "normal" road use so I dont see the point of them really...................................