Had my Brabus for over a year. I've so far done over 12k miles. Only problem I've had with it is droning/humming noise from rear from new. Diagnosed as problem with rear axle bearings and/or suspension mounting bushes. Dealer replaced bushes under warranty, no more noise and ride kinda improved and a lot quieter.
A known issue with a lot of early cars was the extending door handles would not fully recess, stay open, not open, etc, but most if not all would be fixed under warranty. My car didn't have this problem until a couple of months ago when both the front door handle started acting up. Waiting for parts to arrive to fix.
Initial problems with software but mostly ironed out along with a lot of improvements after ota updates. Ver 1.5 presently added V2L which has come in handy for me on a couple of occasions.
The Hello Smart app is pretty basic and can be a bit buggy but I only ever use it check if I've locked the car and if it is charging. It randomly logs you out which is annoying.
Proximity lock/unlock feature is a bit temperamental but it works 90% of the time. Of the 2 keys, one of them drains battery abnormally quickly so I use the other one with no problems.
I was fortunate that my car was well put together. Panel gaps tight and consistent, paintwork was nice with no noticeable orange peel effect. Interior was also solidly put together. No squeaks or rattles from new, but it has developed rattle sometimes now when the cover over the charging pad is open. Also occasional buzz coming from when the cover of the cup holders is open.
The car has never broken down, no electrical faults, drives as nicely as it has when new. On a couple of occasions I've left it parked unused for 3 weeks, came back, battery lost only 2-3% charge, car started and drove away no problems at all.
Overall I'm happy with the #1, would be even happier if it had longer range.