My Borg 45ED II needs the NGF-S for fine focusing and also to reach focus. My C5 can be used without the NGF-S, but it will be better with it especially for high power imaging, however, the C5 is a bit too small for the NGF-S so that its base cannot fully sit on its SCT thread adapter due to the original focuser knob.
I just found that I can solve the problem like this:
1. Borg 45ED II: to use a 2" visual back behind the rough focusing draw tube of the Borg
2. C5: to use a 2" visual back which will raise the base to avoid contact with the original focuser knob
So, to attach the NGF-S to the above two setups, I simply use the SCT thread adapter, together with a 2" to SCT adapter, so now the NGF-S can be placed inside any 2" visual back! In that case, I can easily remove the NGF-S from one scope to another, just like swapping an eyepiece, and the C5 issue can be solved at the same time. I found that my C5 has enough focus travel, of course, the downside is that the C5 will be rear heavy and with the added length of the NGF-S + 2" visual back, it will away from its optimal optical configuration, it will be like f/11 or even a bit more due to the moving primary.
But so far, it seems the best workaround.