I’ve got the “Hot Hands” from the same web site.
They’re fabric hand (grip) heaters that just wrap around the existing grips with velcro type material and can be easily removed in the Summer.
They work well for me and I’m now into my second winter season with them. Just be careful to put the colder area (where they fasten) in the area uncovered by your hand or fingers.
Heated Grips are good, but I also recently bought some First Gear Carbon heated gloves and find that for the really cold days, both grips (inner hand) and gloves (outer hand) are required to keep my hands warm.
If you wired the grips directly to the battery (not via the ignition switch), be sure to always check that you’ve switched them off when leaving the bike. I inadvertantly left mine on one day and came out to a flat battery.