Mike, that device (and thousands of others) are carefully designed...to remove dollar bills from your wallet.
Beyond that, it does nothing you can't already do with a variety of other (free) methods. As Jim said, if you want circle shapes to use as a guide, cut several out from cardboard. Personally, I use a compass. I find the approximate center by eye, and draw a circle. If the circle isn't centered, I move the compass point accordingly and draw another circle. It doesn't have to be exact...your lathe will handle the "perfectly round" part for you.
The woodworking market is full of gadgets. Some are very handy, some are kind of useful, and some are junk. For the most part, what the gadgets do can be done without them. (And in some cases, it can be done more easily without the gadget.) Now I
do have a lot of these gadgets myself, so I speak from experience here, but every once in a while it's good to remember that even in today's world with lasers and GPS and high tech everything, the finest brick walls are still built with just a piece of string and a bubble level.