Yes, they're a bit chewy but you soon get used to that. When I was a student at Harlech, we used to cook them in their shells, on the hot ashes of a fire, on the beach. You just have to be careful of where you collect them these days. Check for sewer-outlets first!
Since then, I have them in soups and fish stews too. Mind you, it takes awhile to develop the knack of getting them off the rock!