There are good and bad service anecdotes for BMW or Zero. The BMW C evolution looks very mediocre to me for that price - it needs faster charging, more power, more range.
I think a lot of "bad service" is the responsibility of the dealer. My local dealer San Jose BMW/Zero has been poor at normal motorcycle stuff. The dealer says Zeros are not hard to work on, but it is specialized.
My experience working with Zero directly has been really good. I'm local to the headquarters, so I can go there for help. Zero is a lean operation, so I can imagine that if they are doing all the dealers work, they can get overwhelmed.
Its hard to have good data on reliability numbers of Zero, but from EMF and FaceBook, it sounds like Zero has software and EV hardware gremlins. My Zero has been good, but I have experienced some occational gremlins and the dealer has had the bike for a week and have not found any solution. The dealer is closed today and tomorrow, so Tuesday I will see if they have any solutions.