Hey those are good prices for diffs! Definitely required if you intend to turn your trike/quad in many situations. In my case, I wont be permanently mounting the 2nd bike. I won't need a differential simply because there will not be an axle at all. What's going to be more important on my particular build is the steering will want to bind when I turn. The inside wheel needs to turn sharper then the outside one while cornering.Instead of 2 motors get a differential axle, both wheels pull and ratchet in comers. https://www.staton-inc.com/store/index.php?p=product&id=179
You can get 3/4" also. https://www.surpluscenter.com/New-Arrivals/Peerless-100-007B-Differential-3-4-Axle-13-1618.axd Welcome aboard..............Curt