Take the DIY method, you have more $$ for ingredients
Also, looking on their site, that ferment kit is out of stock, as well as that heat wrap thing - but, check out the others on fermentation temp control page
Johnson controller - $52.99
States for fridge, but would also work on a heating element; range is 30-80 F. Could use it for fermentation control for brew belt, fridge fermenter, or keezer.
Digital Temp Control - $79.99
Same as the one in the kit, a wider range of -30 to 220 F.
Brew belt - $22.50
Either way, cheaper then buying the kit (add a 'thermowell' stopper, or drill out a stopper to feed temp probe through). Either of the controllers are temp based, and just turn the plugged in appliance on or off; use the brew belt or make a chamber with heat lamp/rock etc!