I bought an installation kit (E-Bike Conversion Kit 36V 250W 28"(700C) Front Motor Kit with HL1 36V 18Ah Battery Hub Motor DIY) and have installed it. I've ridden the bike for 60 km now and the battery retains power well. The system seems to work very well. The installation was reasonably easy, removing the crank arm was a bit difficult because it was tightly attached (the crank has never been taken off, and the bicycle is nearly 30 years old). However, with the included tool, the crank eventually came off.
When reinstalling, I noticed that the PAS sensor is slightly too thick, and the crank arm can't be fully tightened, which causes it to loosen after a short ride. I might need to order a different type of sensor. Also, the mounting points of the battery holder did not align with the bottle cage mounts on the frame.
Nonetheless, I am satisfied with the product. PB Finland