Yep Marc is correct. Your FOV at F10 would be the same as mine but you would have 12 inches worth of photons crammed down to your camera. So you would have an advantage over my set up. Although the OAG takes a small proportion of those photons you would have ample to get a guide star.
I even experimented with solving from the OAG image and was able to do this more often than not. So this just shows that there are plenty of guide stars to play with.
Technically it is not difficult and as you are already using ZWO cameras the ZWO OAG is designed to make it easy to get the correct back focus.
Once you have got it parfocal with your main camera it is a breeze
.
The other advantage is that you don't have to bother with having the extraweight of a guide scope. The really short FL ones will be a real struggle. Flex can also create issues with guiding that you just don't get with OAG.
Hope this helps to reassure
Mike