I have a set of these for £99 cant fault them. Did some research before buying and didn't really heard a bad word Race-Tech Tyre Warmers £99.96 | eBay
I had some and thought they were shite. They work off a thermostat and the temperature is up and down like a whores draws. The Mrs got me a set of Capit Superbike tyre warmers and I found them far better. They hold the temp at 80 deg C constantly. I know its all in the head but if your tyres are nice n toasty to the touch then you don't ponce about warming them up for a lap or two.