I have Gerbing heated gear. Jacket liner (8 amps) and gloves (2 amps). I ride throughout the year and feel the cold after an hour or so. I have now used them nearly all day on a bullet 500, without any power drain problems. The jacket liner is warm at setting 3 of 5.
The real beauty of heated kit is being relaxed in the cold and not having all the layers restricting movement. I ride with a long sleeve T-shirt, liner and leather jacket. I think this will be the best £300 I've spent. The Gerbing kit is not the cheapest, but not that expensive compared to insulated winter gear. It has good quality materials and connectors and a lifetime warranty on the heating elements. The only downside I've noticed so far is, when I ride with mates, they need to stop, to warm up. That's when I get cold!