Very happy for now. Received yesterday, I tried them one time each. They all work. It takes a little time for the start (shake pdt 20 s and push the mine several times) but after it works well. It should be clear with a cloth or damp sponge (dry it does not clear). For now only tested on a regular slate. See use in time (if they are emptying quickly, if they can be used on all surfaces, ...)