The Satin Snow GG on my Speed is quite good. I’ll admit being apprehensive about changing out the original gg with respect to possible spacing errors thus focusing problems. Dave gave me his personal guarantee that his product would work and IT DID!
I have been very happy with his product and will order a back-up soon.
In the past, I ground mirrors for telescopes and thus experienced the trials and efforts involved in working glass. It ain’t easy and requires diligence, great effort, and experience. Dave’s products reflect these qualities and cannot be rushed. So, if you are interested, Please be patient.