I saw these at the local store and thought they might come in handy, but wanted to ask to see if anyone has used them before. They are little flash units that will sit on a flat surface and have their own tilting stand or you can attach to a camera or tripod. They work by sensor so that when main flash goes off, they go off. Thought it would be good for indoor shots of my kids. They are really inexpensive at $20 each. Any thoughts?