Well, for wide field, its unnecessary methinks. Ive done a lot of testing and have seen a fair bit of drama to do with automation (far to much
), your heading for grief with an OAG generally. Also, its expensive to automate OAG rotation to find a guide star, and youll need plate solving and integration with The Sky (or a guide star catalog) to do it properly.
Yes, flexure is a problem, but guide cam focusing isnt, at all. So I bolted my guide cam to the imaging OTA to (almost) eliminate flexure and shift/movement and havent focused for 2 yrs, its irrelivant. Focus once and forget about it.
Unless your doing 15min plus exposures at more than 2m FL and are a precision fanatic, external guiding is MUCH easier, very especially if you want to automate your rig.