I have a front Staton friction drive, a front BikeBug(untested), rear Staton and BMP housings. Also a Staton chain drive and scooterguy midframe/shiftkit(untested).
I need to have the power to keep up with traffic. If not, it is too dangerous here to ride a motorized bicycle. If I need to pedal, I find safety on sidewalks, but I ride slow and ALWAYS ALWAYS give the pedestrian a lot of room and respect.
Like the OP referred to, I'm the guy with the high-powered rocketships on cinder blocks. LOL. Senior citizen life keeps me busy, and so do my projects, my fulltime job. and night school. Thank God the kids are adults.
I've probably worn through more rear tires and had more flats than anyone on this site. Probably swapped more friction rollers than y'all too. BMP housings are infinitely easier to change bearings and rollers than the other guy. Staton has an excellent 1.375" and 1.5" roller. You can swap them into BMP housings by changing clutch drums, spacers, rollers and bearings. It is simple enough to sand down the roller ends just enough to change the press-fit to slip-fit. You can now change rollers and bearings in less than 2 minutes, whereas swapping spindles and bearings in the other guy's drive housings cost you a day's downtime and $80 EACH TIME you do it. Bearings at a gokart online site costs $4.50/pair, whereas one vendor sells them for $13.50/set.
Haven't tried the axle mount or NuVinci yet, or Happy Time stuff.
For the bulletproof combination, I'd choose Staton chain drive and Mitsubishi TLE43cc engine. However, changing rear tires are a royal pain.
Changing rear tires OFTEN on friction drive is a royal pain also. They wear through quicker because of the road surface materials and wet weather.
Climbing medium hills with a 1.5" roller is an effort on a single-speed bike, but no biggie with multi-speed bike. A 1.5" roller on the flats is the bomb.
Climbing hills with 1.375" roller is easier, might be the best all-around roller.
My first MB had a Subaru 1.6hp engine and 1.125" roller on a Dahon folding bike. Good starter bike. A "widowmaker" with 2.2hp Mits engine and Staton chain drive.
In my opinion, the best combination would be the scooterguy midframe/shift kit setup with Mits/Honda/Tanaka/Subaru engine. Not particularly keen about the long, exposed chain, but tire access would be same as regular bike. Tire wear would be excellent.
I'm guessing that the ultimate setup for me would be a midframe Japanese engine with short chain and SBP/shift kit.
Vendors should probably come up with this next.