I have never owned a 'set' of pans. All my pans were bought individually for a set purpose. I do have a double boiler and have since I first got married in the late 50's. I use it all the time. It is a Revereware with a copper bottom. I stopped shining the bottom years ago. Nobody but me sees my pots, and I don't care what the bottom looks like. I tried melting chocolate in the mike just once. A disaster. It burnt. Back to my trusty double boiler. My first husband was a pro chef and he is the one who insisted on having one in the house for all sorts of use. I also have a Stir Chef. You attach it to your pot, set the speed and it stirs the pot continuously so you can step away for a minute or two.
I also make lemon curd in my DB. Along with other sauces. One year I poured all the turkey juices into my DB attached the Stir Chef and walked away while I did the mashed potatoes. Perfect gravy. I also bought at a separate time, the steamer top for the pot. Great for steaming veggies. One of the things I like about the Revereware is that (except for the DO) all the pots are the same size on the top. The differences is in the height of the pot, not the opening at the top. So the DB and the steamer will fit on any of them. You cannot use the top of the DB alone on a burner. The bottom is not thick enough to prevent burning your food. Not even on simmer. It is a one use only utensil. You must use it with the bottom.