Guys-
Before spending big bucks on chain tensioners, do yourselves a favor: shorten the motor side chain using a chain break tool so there is no need for an ugly, weak tensioner. On the pedal chain side, shorten or lengthen the pedal chain. Using "half links," which you can get at a bike shop or online, you can get the chain length just about perfect. It's clean, simple and direct, with less parts to worry about. It's cheaper, too! It takes some patience, but it is well worth it.