If I were to use my mitre saw for cutting pen blanks, I would probably just clamp a stop block in place and use it. Although that puts the hands mighty close to the big 10+ inch spinning blade when making the cut, so I might also use a push stick to hold the blank in place and keep my hands farther away.
The PSI unit looks like a useful tool and isn't too badly priced. And watching the video it seems simple enough to use, although I question it would be faster than a simple stop block if you are cutting several at once - It takes time to lock and un-lock the blank with the set screw they incorporate. And yes, round blanks could be problematic as well.
However, all that said and having a small bandsaw in the shop, I prefer to use it instead as I feel safer using it for cutting small items like pen blanks. Set the fence using the tube (adding about 1/16th of an inch for truing) and then pushing the blank through using a push block with a 90 degree edge to ensure the blank gets cut straight. This routine works fine for the round blanks as well as the square ones.
All my "wordiness" aside, and to answer the original question as best I can: I don't have one, and I don't think it's the best way to spend your money for the simple task of cutting blanks. There's too many simple shop-made alternatives that will serve you just as well and keep the money in your pocket.
