I prefer the ScopeStuff 2” nosepiece with inset 1.25” filter threads. It is a c-mount nosepiece and has the 2” threads at the end of the nosepiece while the 1.25” threads are inset in the nosepiece.
The reason for the preference is choice of filter sizes and more importantly - I have not found any 1.25” focal reducer that doesn’t vignette. Because of backfocus issues with most NV devices, the focal reducer is usually put on the end of the nosepiece (after the diagonal rather than before it) and while it may not give true .5x reduction, it gives dramatic reduction and have found no focus issues with my telescopes. I found the Antares 2” .5x reducer works well in all of my scopes (AT72ED, 120ST, AT152, mak 150) with all my NV devices (pvs-7, pvs-4, Litton M942, NVD Micro, NAIT NVPS-10) and doesn’t cause vignetting.
part# is #C2BF - C-Mount to 2" Eyepiece Barrel Adapter with Filter Threads
it is $44
I have a 1.25” nosepiece as well but doesn’t get used much for reasons I stated. I use the Antares reducer about 85% of the time when viewing in Ha narrowband. The difference for me is in my 120ST at Native F/5 the Flame nebula will show up but can’t see the Horsehead. With reducer in, the HH will even show as a lump in my AT72ED. Many threshold objects become more detailed or even just become viewable with the reducer. My location is heavily light polluted though (white zone with some access to red zone conditions coastal).
Using a 2” nosepiece also gives a little more backfocus room as the 1.25” adapter extends the mm to the device. If going with strictly 1.25” diagonal then it is a non-issue as it doesn’t increase optical train length.
Maybe one of the experts will chime in here on this thread though.