They arrived a couple of hours after this. They're reclaimed tyre rubber. They look nice, and they're nicely grippy.

Unlike the ones that RobS has, they don't have any "teeth" on the bottom -- apparently they're supposed to sort of bed themselves in over time.

In the downpour today, I discovered that this is not exactly true -- as I surfed a couple of feet across the lawn on an errant slab.

I'll look into cutting out some turf and bedding them down properly on either sand or gravel.