For most of my pot melts I kiln washed terra cotta saucers and they worked really well. I too was concerned about abusing the kiln shelf and found these saucers extremely successful. Depending on their origin, some seem to last much longer than others. Some of them cracked after only one use, but many I have used several times over and no cracks. The beauty of these besides being very inexpensive, and the variable sizes, is that the pot melt doesn’t stick at all and comes out with a very clean bottom, as opposed to when it flows onto the kiln shelf. Seems like it takes part of the shelf off and is very difficult to remove from the glass. Lots of elbow grease or grinding to get the shelf material off.
Also there are no worries if you used too much glass of it dripping on to the floor of your kiln as it’s all beautifully contained in the flower pot saucer.