Isn't it common knowledge? 40% of employees work in companies with a worker council, it's pretty much the default for large enterprises.
I think it's pretty accurate regarding career effect. Worker Council members are generally much more union-involved, which employers obviously don't like too much. On the other hand: as long as you're a member of the worker council, you can essentially not get fired at all (short of being caught stealing or physically attacking people) so it's a stable career in itself, though rather like working for the government: you won't get to the highest heights, but you'll also not have to work too hard or fear for your job in an economic downturn.
Among german-native workforce? Probably. Among the huge swaths on immigrants in Berlin's startup scene? Absolutely not.
If there's one good thing that's gonna come out of the idiotic attempts by the N26 management to stop this, I hope it's bringing more awareness to the fact that "Betriebsräte" are even a thing that exists.
Second step is getting help in actually creating one, and I'm hoping that ver.di (and other unions! IG Metall has been active in this space recently too.) will step up and provide guidance and support for this.