This was the very first blender pen for me. I still have it after 5+ years! I also still have the refill, which I highly recommend you purchase. Is there any other refillable type pen? I have not seen any other than this one and it just makes so much sense to reuse the pen you buy.
There has not been any problem with a single pen and multiple colors. Just use with your color then "erase" the pen on scrap paper, add your next color. Use with chalk, watercolor pencils/crayons and waterbased markers.