That Rail 29" looks like the chainstays would interfere with mid-drive motor's chain rings. You're better off looking for an older - prob. 26" wheel - mtn bike with a long chain stay length (where chainstay widens for the the wheel clearance further back). Modern mtb geometry often has as short as possible chainstays that widen immediately (and a lot to clear fatter 2.6-2.8 tires). I recommend going with the Bafang BBSHD. The TDZ16 may have solved these problems but all the predecessors had issues with stripping the nylon gear and with torque sensor failing. The BBSHD doesn't have torque sensing but I don't find it a problem, although I don't ride on mtn bike trails with it (too tall gearing for that anyway). In 2016 I built an (approx. 2008) Norco Charger (26in wheels) with a Bafang BBSHD. I bought a 130mm BCD spider adapter off Aliexpress and a 44t (or 42, I forget) chainring to bolt to it to replaced the stock 46t steel chain ring - to get better gearing, save weight and get better chain alignment. This helped inboard the chain alignment slightly to correct the chain dropping off the front chainring sometimes when in the largest/easiest cog (chain was angled too much). To completely solve the problem I got a cheap shimano 8spd cassette that can be disassembled and I moved one of the middle cogs to the far inside, effectively deleting it and using it as a spacer that re-positioned the larger cogs outward. Apparently the Gustav replacement chainrings for the BBSHD have a large offset that inboards the chain further so the cassette cog move that I did may not not be necessary, depending on the frame. The bike works fine with 7spds. It has been very reliable. I ride it everywhere in the lowest power setting and have no problem climbing the steepest hills in 1st gear (many hills where I live). Is important to replaced/repacked the grease when it is new (is easy to do - google it). The other key reason to go with the BBSHD is that custom and replacement parts for it are readily available and quite cheap.