I think the third party dashcams are better. Smaller, more discreet, and with more features. I've been using the blackvue dashcams for years, and just installed the 900s on all 3 bimmers over the past week.
I just saw something about BMW drive recorder, which I think utilizes the built in cameras for recording?
If this is indeed the case, I think that is definitely the way to go. I'm surprised it's taken this long, and hopefully it will be an option available in the near future.