[bojan]

On my 10" I am using what bintel is selling as orion finder, the diameter of the reflective lens is ~20mm and it is quite sufficient, however the new one will be better, being 40mm in diameter. I haven't used the finder very often since, and only for the precise pointing of the camera.
The only slight problem with all those sights is tinting, it is a bit too dark and blue coloured to enhance the reflectivity of the red dot (so is Orion..) but they are designed as rifle sights, not for astronomy use anyway. I guess Telrad is not tinted ?
I was playing with the idea recently to replace the reflective lens on one of those sights with the lens made from plastic safety goggles, they are clear and reflective enough for night work, and the curvature of the surface seem to be adequate....