Where to mount cadence sensor

[Slacker]

Trying to upgrade on the cheap.  Picked up a Chinese cadence sensor, works great but instructions are in Chinese.  Shows two positions to mount, crank or hub.  Hub seems better, any downside?

Edit: haha, upon thinking about it it has to go on the crank, not sure why they show it on the hub.

[karlos]

Hub doesn't make sense. Cadence counts pedal revolutions, not wheel revolutions. The instructions may be confusing. I've mounted several cadence sensors over the years. Btw, best I've had so far is Wahoo. Mounts on the crank and uses accelerometers, not a magnet pickup on the frame that must be just a few mm's from the sensor as the crank rotates. Does yours have a pickup or does it also use an acclerometer? How about attaching a photo?