They work
Plumbing and hardware stores used to give a few of these away for free, or for just a few cents each.  I looked recently and could not find them.  Now I have more than I will probably need for the next ten years, but it is worth it.  They work.  Saves a lot of time in determining if you have a toilet seal leak, and whether or not you have been successful in fixing it.
Rating: 5 stars