Used to use whilst eventing but haven't for about seven years (not evented for that time as too old, too arthritic and now too fat as well!) - the variety attached to the rug (magnopulse???) that you plug in were fab but expensive and certainly helped with lymph and the general circulation in the legs. Never been too convinced about the standalone type....bioflow etc.
Can recommend the bioflow bracelets for humans! I wear one all the time and if I don't wear it then I can barely move!! Haven't used the boots but if they are as good as the human stuff then I think they will be fab!!