There are lots of good diagonals available, but I know of only two which top the list. I favor the MaxBright because of Astro-Physics confidence in their mirror coatings. Although we are constantly warned against excessive cleaning of optics, this company advises us to go ahead and clean the mirror if necessary. The final proof of the product is what you see in your scope. I see a definite improvement in clarity and definition in views when using the MaxBright.