1- The pedelec sensor will not damage the controller.
2- Other sensors may or may not work with the vector controller as some have a pulsed signal output like the GM sensor, but others have a variable 0-5V output.
3- If you don't have the BAC-601 Smart Display unit the pedelec will always be turned on and you cannot adjust the assistance level without using the programming lead and you would need to disconnect the sensor to turn off the pedal assist.
With the BAC-601 Smart Display you can select the assistance level from 0 to 5
(where 0 = no assistance and 5 = maximum assistance) using the separate mode button mounted on the handlebars:
The controller on early MP4s would not work with the Pedelec sensor, but as the effected controller numbers have not been published there is no easy way to determine whether yours will work until you actually try it.
If you decide to use a non GM sensor and it works then that's fine, but if you use a non GM sensor and it doesn't work, you will have no way of knowing whether it is due to a compatibility problem with the sensor unit or whether your motor has an early controller fitted.
If the controller needs to be replaced, it should be possible to upgrade your MP4 by fitting an MP5 controller
(and the plug-in Bluetooth unit) to allow pedelec control via an Android 4.4 or higher Smart Phone
(currently awaiting release of the iPhone app):
Unfortunately, the five power levels are not as progressive as you might expect and they are not individually adjustable so I tend to mainly use levels 3 and 4 most of the time.
The biggest problem I find is that the sensor monitors pedal speed rather than pedal force, which means that if you slow down on a hill without changing down the gears, you suddenly find the assistance decreases just when you need it to increase.
If I didn't have the Smart Display unit
(or a Smart phone and Bluetooth unit) I simply would not use pedal assist at all, as the only option would be a single "fixed" level of assistance that could not even be turned off easily, although some riders I know would prefer a more basic option.
Alan 
