Put 1500kms on my ES1-300 so far. That’s probably about it as my Phantom came in today!
I’ve had my fair share of problems with this scooter, but have been able to keep it going for almost 2 years now. Just like the ninebot ES2/4, the weak point is the controller board (in the shaft under the battery). There are great disassembly videos on youtube about this. Just make sure you search for ES2 or ES4. My summary is that the Regen feature is flawed and litterally melts the control board sometimes. Certainly I made things worse by adding the external battery and loading modified firmware for higher speeds. The regen feature is the E-brake feature, it’s not just the KERS slowing you down.
If you want to try and fix it, just take it apart and hope that it’s just a loose cable. However, given my experience (and 3 control boards later) prepare for the worse. If you do replace the board and it lives, My suggestion is to avoid using the E-brake and just use the rear friction brake if possible. That kept my 3rd board going strong up until the present.