Disclaimer: if you dont lubricate the swiveling piece that comes in contact with the valve's face, it will eventually bind up and cut a nice ring on the face of your valve. I used redline assembly lube, you can use whatever works, just make sure it spins smooth and easy when applying pressure to it with your hand.
That out of the way, good tool. Theres tricks to using it in my experience. When installing valves, I find myself pressing the black handle against my stomach to keep one end on the valve spring, holding the tool up with my left and centering it on the valve face with my right.
Pics: the part that needs lube, the ring caused by not lubing said part, and a kit I put together for valve lapping.
Product list: Loctite clover fine grinding compound, redline assembly lube, acdelco gear marking compound, and in the corner is a phillips screwdriver with a piece of 1/4" ID fuel line jammed on it to grip the valves from the stem side. just get some of those blue lint free shop towel rolls and some rubbing alcohol for cleaning.