i went with a hub motor because of the cost/relative ease of installation. I have had it almost a year now and here some thoughts/suggestions.
for the donor bike, I would lean toward a frame that has horizontal drop outs. Mine is a Specialized mountain bike which has vertical drop outs, and keeping the wheel in the frame has been a challenge. I am sure somewhere there are torque specifications on the subject. Ultimately, locktite and torque arms solved this. I would suggest torque arm on both sides. Grin Technologis makes a beefy one. I wish someone would devise a means of securing these things with something besides belt clamps.
I have the optional GM LCD screen. It went through a period where it had an error code 9, and wouldn't allow the bike to function. I could get around it be unplugging it and either plugging it back in repeatedly or just not using it at all. After a month or so, it finally went back to working correctly on it's own apprently.
A hub motor is heavy, and hard on spokes in my experience, so I would be careful jumping curbs or riding on ungroomed trails. Oddly, I have had over half of the spoke nipples come loose or completely off. I never had this happen with any of the motorcycles I ever owned. Luckily, they are trapped inside the wheel and can be recovered. Unluckily, because they are aluminum you can't use any magnetic tool to hold in place to get started on the spoke. My solution is to enlarge the access hole for each spoke with a drill bit and use a surgeon's hemastat to put back on the spoke (with loctite) and tighten down with a small flat bladed screwdriver. I can tell when one or more is loose because the back end feels mushy, I assume from the other spokes flexing. if you can see the threads, you probably should check for tightness. When I bought this kit, there was no option to have it laced with higher quality spokes.
I have the bottle type battery. Due to the number of times I had to take this thing apart to fix the spoke issue, I made up a quick disconnect between the battery and the motor which may save you some time.
I weigh around 190#. I get almost 29 mph on a flat, hunkered down to decrease wind resistance. I have the 13AH, and can go 25 miles for sure. I only run it down to 3 bars (out of 5) and go 18 - 22 mph most of the time. I added a larger crankset to help get the speed up.