I test rode a Pendix before buying a ready-made ebike. Decided against it as it
a) was wide i.e. large Q-factor such that my legs felt like they were splayed out. Not good for my knees. Possibly it would be better for those with wider hips (I'm only 170 cm).
b) felt weird. It's direct drive and very responsive to pedal pressure. This means that the motor is on-off during each pedal cycle with a distinct thrust each time you press down. A conventional bottom bracket motor (Shimano or Bosch) is much smoother as they have smaller diameter armatures spinning faster therefore have momentum to smooth the power delivery. Either that or different electronic control systems.
That said I really liked the neat design and simple control on the battery. Bit expensive though for an add-on motor but being German well engineered and should be reliable. The shop where I tried it had given up on Bafang as 30%+ were being returned; some batches were good but others very poor with electronic faults.