The DLC missions for for this (Lost Harvest) were a mixed bag, but now I'm done with those I can finally build the treadwheel and this thing is fun.
I'm running on a console so, this may not be usable with a keyboard. Even with a controller, it can be a little hard to control at times but once you get over the learning curve it's a blast. Turns on a dime, launches like a stunt bike (doesn't fold front first like the sandbike), and attracts less attention on the open sand. I've only built the basic version so far (Mk4) but it can top 100 with the thrusters kicking.
It's a novelty item yes, burns fuel like crazy, leaves you exposed to the elements, and it's no doubt gonna get me killed sooner or later but worth it for shits and giggles. Also looks damn cool in the garage.
One thing I would have loved to see: independent control of each wheel using the two triggers. The shoulder buttons could then be reverse, allowing for some crazy donuts. Would be an even harder learning curve (maybe make it an option) but I think once mastered, this thing would be awesome. As it stands today, they seems to have modeled the physics pretty well but the controls are suck in classic race car mode. That's an update I'd love to see but until them I'll take it as is.