I have the of-fh, not the mortisepal (I do have a domino).
I use the of-fh mostly on doors. Routing slots in doorbottoms for automatic anti-draft strips; slots for the guideblocks of pocket doors; Mortising allong the long end of the door for multipoint locks, mortising frontplates of standard locks (it does a good job of keeping the mortise square to the door itself when the door is beveled).
The mortisepal seems to be focused on mortising for loose tennon joints, I guess you can use it for longer slots, but you have to move the jig alot. The of-fh can be used for such mortises in a lot of cases aswell, but you have to mark the position of the edge of the of-fh at the beginning and end of the mortise (or clamp stopblocks at those locations) because allthough the jig, and dustshroud of the router are transparant, you cannot view accurately where you are routing. (As an added opportunity for F-ups, the edges of the of-fh do not have the same distance to the centre of the bit)
The attachment point for the vac hose on the of-fh works adequately, but only for long grooves. When I bought mine, festool advertised the thing as a"universal" routerguide that could be attached to other brand routers aswell. But if I wanted to attach it to my Bosch plungerouter, I would have to remove the dusthose hookup thingy.
The mentioned thingy is sized the same as the thingy on the TS saws... 27mm hose fits inside; 36mm hose fits over (recommended), so if you have an adapter to fit the hose of the fein to a TS; it will fit the of-fh aswell.
BTW If you like the functionality of the of-fh, but the price is above your budget, you can also use long rods with an edge guide on both sides of the router; or make one yourself; there's a well documented thread of someone doing just that; you can even order most of the parts from festool as a replacement part. (I'll do a search and post the link later)
