I don't have a E-bike yet, still shopping and the RR is on my list. How are the fat tires compared to road tires. Are they smoother depending on the air. I've heard they can be let down really low. I'm not near sand but they look so cool !!
I have a bike with 700X40c tires set around 50-60 psi and the Radrover set around 18-20 psi. Both bike have front suspension and I just transfer my Suntour SP12 NCX suspension seatpost and Sunlite 12.5X11.5 Cloud-9 seat between them.
The Radrover is so much smoother on paved road because the fat tires can soak up the road imperfections compared to being transferred to the rider like my 700X40c bike. The Radrover is very stable and comfortable at 20-22 mph on paved roads for my morning commutes. You do have a lot of road noise from the RR tires; but, you quickly get use to it and I don't even think about it now. I spend more time sitting on my seat with the RR during my 6.5 mile commute compared to always lifting off my seats for road imperfections with my old bike. I have to ride main roads, side streets, sidewalks, paved bike trails, and across a dirt lot and the RR makes each transition at speed without missing a beat. I would suggest a suspension seatpost like Thudbuster, bodyfloat, or Suntour. The standard seat is comfortable; but, the Sunlite Cloud-9 is extremely comfortable (never ever had a sore bottom after +3 yrs of use).
I've ridden both bikes on the hard packed, rocky, and/or sandy trails and the Radrover does a much better job off road. I just set the PSI to around 10-12 because the trail can go to hard, rocky, to sandy very quickly in the southwest. The advantage with the PAS and throttle is when negotiating rock and tight turns. On a regular bike, the pedals would hit the rocks or you can only coast around a tight corners. I love having the throttle to keep my speed and power up negotiating obstacles and tight turns. You don't get the front tire dig-in on sand like you do with a thinner tire when you turn the front tire.
I've tested my rover in extremely loose and dry sand that was about +4 inches deep. That would have been 100% impossible for my 700X40c bike to ride through. It was extremely slow going, I had to stand up to pedal, and my motor was maxed out (don't think I could have made any progress without PAS). I was worried I would overheat the motor and I was 6 miles from home (decided to walk the bike to harder ground).
I would also suggest tire liners (Mr. Tuffy) with sealant (2-4 oz per tire of Stan's tire sealant). The 4" fat tires run over a lot of debris like wood splinters, sharp rocks, broken metal, thorns, and broken glass at 20 mph on the side of the road that would cause a flat on an unprotected tire.