I used some sale stuff from Joanne's but the finished block feels hard under the applique. Now I'm using plain old cheap dollar store school glue, ironed on and then stitched around the edge with a tight zig zag. Then the glue washes out and the block is just as soft as if I had never used the glue!!
I've never used any other of the iron on stuff so never knew much about different ones. My Grandma taught me to sew, she never had any of that stuff, she used old magazines that folks gave us, also Montgomery Wards catalogs to cut out her templates.
Sure wish I had her old treadle machine now!