I had one of the first Hind Sights that they made and while it worked, I had to be very careful at other yardages above 20, instead of putting the next pin in the center of the X I had to keep the 20 yard pin in the X then raise the next pin to be on target.

Another bad point of it was my sight picture was now very cluttered.

IMHO the Timberline No-Peep is a much better option as it clears up the sight picture plus lets you visably see when you are torqueing the bow or if you have not hit your anchor points.