My first impressions were that they were quite small and they didn't seem to be very well made. Once I started to use them they seemed reasonably soft but I had a problem getting them to adhere to the paper. This meant that I had to fix them before I could put anymore layers down.
My colour selection was limited so originally I decided just to do the best with what I had but in the end I decided to finish the painting with my Stabilo pastel pencils and Koh I Noor soft pastels.
Another thing I didn't like about the prismas was their smell. It seems to cling up the nose.
Although they might work better on different paper or board they really weren't to my liking.