I use my pounce all the time, and absolutely love it. It is my favorite way of marking.
I make my own stencils by drawing designs on transparency film (If you are a little older you would know it as overhead film sheets), then sewing (without thread) the designs. I then rub the pouncer over the film and there is the mark. I have never had any trouble getting it off and usually it is wiped off too soon and I have to re-mark, but if I do get it in the wrong spot and I want it off now I use a slightly damp cloth and it wipes right away. I have only used the white chaulk, never the blue so I do not know how it would come out.
The trick to remember is: Although it is called a pounce, you wipe it across the stencil.
Friends have borrowed it to see if they like it, and some really like it, others don't. It would be great if some of the other quilters that you know have one and would loan it to you for a test run.
Aileen