The west side of Milos is full of interesting beaches. I was planning to visit places like Ammoudaraki by quad, which seems fairly doable according to the YouTube videos I've seen.
However, I find contradictory information about whether the rental companies allow using the quad on the unpaved roads of the island. Do some companies allow it, while other don't? And what does "disallow" mean in this context - is it that you will not get any emergency road service?