MDM is safe if you're not sure what you're doing behind the wheel and you're going for the fastest lap vs. kicking the backend out with traction off and having fun.
I would say at least half of the accidents that happen on the track are because the drivers too confident and loses control of the car. MDM makes sure this ^ doesn't happen.
when I have MDM on I get faster laps just because I can keep on the throttle and let the computer work its magic, but usually keep it off..It's all about how much experience you have I guess.
2008 M3 Sedan + catless + Tune
2012 CLS63 AMG
2014 M6 Coupe + catless + KW V3
2015 Porsche GT3