I have one, for the most part they're worthless. You don't need a rev fire to know whether a pitch is spinning enough. On top of that, the axis is as important as spin rate and the RF can't help with that. I've seen balls spin at 25rps and not move an inch off of straight. Put a stripe on the ball, listen to the seams grip the air, watch it move. Movement is a combination of spin, spin axis and speed.
iPad Pro for me, shoots 240fps. Quick enough to catch the release. Load Coaches Eye and RightView Pro with all the Pro Pitchers on it. Do side by side comparisons so the girls can see with their own eyes. Invaluable.