Been a while since posting. Belted or Direct drive is down to personal preference here (there is no real difference in performance between the two, just a myth). My opinion on the potted motors is that they can be a hit or a miss when it comes to wear and tear. especially a worn commutator as these machines were probably used a lot more frequently especially when table mounted (my opinion only, no proof on this). It can be hard to find a replacement comm or a properly serviced motor for these.
This is where the belted motors come into their own, as mentioned....modern motors can be purchased for these if the original motor is shot.
I also agree with the others on the model 15 over the 201, much much easier to maintain. The Class 15 bobbin also holds more thread over the Class 66.
ps: my fav machine - 15-91