I was fortunate to be able to find a couple of the Niji (Yasutomo) GRIP500 pencils after they went out of production in (I think) the early 1990s. There was nothing like them before or since. If you can find one, pay what you have to for it, but make sure it is NOS or in perfect condition, and do not try to take it apart to see how it works, because there is some non-obvious trick to reassembling them correctly.