If you already have an extra power strip and soldering gun laying around the house and you are good with electrical stuff then go ahead and get the un-wired t-stat. But if you are going to have to buy everything to wire it then you will end up spending almost the same as if you just bought the prewired version.
All I can say about the Ranco's is that I have 4 of them from RBI and haven't had any problems yet...
Rob