Marseille

I haven't been since 2021, but I go quite regularly otherwise. I lived there in 2017-18.
Fun and interesting: definitely. Both for nature lovers (it's the best springboard for the Calanques, IMO) and for city slickers (the cityscape is unique, and there are some good museums, shopping, charming streets/neighborhoods, etc.).
Safe: it depends. Some areas could be safer, esp. around the station and Noailles market. Single women might not be comfortable. Other areas are largely issue-free.
Friendly: honestly not really, but then I'm not sure what you mean. Many tourist trap restaurants, research is needed before you sit down.

In a nutshell: while it should not be a top priority in a brief trip to Provence, Marseille is a very enjoyable 1 or 2-day extension! Especially if you pass through anyway, as it is a travel hub.