I've been using a TS 9mm thick OAG for a few years now on my imaging train that I swap between a few different refractors. If you're familiar with the ZWO version, it's about the same thing.
Recently a friend of mine lent me his WO Star71 and due to some threading issues, I needed to reset the spacing in my whole train to accommodate the focuser's stock threading that would bump into the prism stalk. It's all sorted now, but it made me think that my next purchase priority should probably be a new OAG- one with an adjustable helical focuser to much more easily get the guide cam parfocal as I try out new OTA's and cameras in the future. I've got about 10mm of space that I can use if I want to use my reducer/flatteners - so total thickness of the OAG shouldn't be larger than 19mm.
I know my options are pretty limited, just curious what you all are using and how much less of a headache you're experiencing from something that is much more adjustable.