I have been using a mini-guidescope for many years. I currently use a Takahashi 7x50 finder with the visual back removed and a non-rotating Borg helical focuser installed instead. I use a Lodestar (original version), and I use Baader finder rings as my rings (allows movement, and VERY precise fit so no slopping or looseness in the rings for the screw jacks). I use a Vixen SXP mount.
I get perfectly round stars each and every time, irrespective of sub-length - a testament not only to the impressive precision of the mount, but also shows - in my opinion - no movement in the guidescope arrangement.
I recently bought a mono CCD. I also bought a Starlight Xpress filter wheel, with integral OAG to go with it. First time I used the OAG I got PLENTY of stars without even having to fiddle or move the prism, just a slight focus tweak. Tracking and imaging with it ellicited precisely the same result as the guidescope image - round stars, time after time. Dithered by 7 pixels per shot now, for both the OAG and guidescope.
So, is there any GENUINE benefit to using exclusively OAG if the system as is produces the same results with a guidescope as with an OAG? Is the hold-over of "OAG is better" only relevant in terms of the "ancient" style of using a large guidescope between widely spaced guide rings?
I know guiding at f/5 is easier than f/8 and above, but is there genuinely any benefit to using OAG in a sagless guidescope system?
For now, my filterwheel OAG has a C thread cap on it as I continue using the finder-guider