I bought this to replace the stock 45° prism that came with my 90mm Maksutov. All I can say is that it is of excellent quality and I always prefer the correct image over a mirror reversed one. I compared the views through the prism and straight through the telescope, and (apart from the neck-craning and upside down image) I can't tell a difference. Perhaps the situation would be more challenging if used with a faster scope, don't know.
I thought that the price was a bit high, but I'm happy with it. If you want an erecting diagonal then just buy this one and you don't need to worry that the prism is a weak link in your optics.
PS. they don't say in the specs but the free aperture is ~24mm as I measured it - very little, if any, vignetting with most except the very widest (absolute) field eyepieces.