I have been buying kalkhoff bikes since i started with them in 2011 with the pro connect model,you couldn`t give me another one because of the impulse motor.I haven't decided yet. While I did like the well integrated, seamless assistance of the mid-drive motor with torque sensor, I think I am going to stay away from proprietary solutions for now.
It's possible to get a very decent push bike (albeit heavy) for £500, and then do the conversion with standard components, meaning the motor can be upgraded if necessary (faulty or better version released), the battery is standard, computer is standard etc. All for much cheaper than the price of a German electric bikes.
I believe the Chinese after market parts are going to become better and cheaper quickly, as they will sell in much larger volumes than integrated bikes. This also applies to batteries and computers.
I now have a carbon Cube hybrid with the Bosch CX motor that i would recommend.The bike has been well used since early this year and there has been no issues.The power comes on a little softer but it builds up nicely at speed and most importantly after the debacle with the kalkhoff dealer it was bought from a fairly local dealer who at least knows how to answer the phone or answer an e-mail.