I'm not very good at darts, but YES, a small slate would be perfect for keeping score at pub and arcade games!
When I originally cut the slate, I did it in such a way that I would end up with two smaller, yet usable sized pieces.
The larger of the two "scraps" was mounted to the side of my kitchen island specifically as a place for messages.
I just mounted that one with "mirror hanger clips" straight to the woodwork. I sanded-down the corners first, so there's no rough edges.
The last piece of slate is a bit smaller than the kitchen message board. I might just use it as a portable/changeble sign, for meeting welcomes, etc.
Here's the big "School Wall" chalkboard in use.