I suspect the D-DIG2D-C-DB DuraBright is simply the latest version of the D-DIG2D-C, with a thicker mirror and "improved" coatings. The D-DIG2D-C is probably old stock.
I have the GSO 2" dielectric, which I use on my Celstron CPC 800: it was a big improvement on the stock diagonal- I saw textbook star images for the first time, instead of funny blurs with the original!
I have also tried one with an LX90, with similar improvement in images.