I’ve got a double seat Trailer with the very same means of attachment, I’ve hauled a 3.5 and 1.5 year old plus kit and picnic bits all attached to a 456 via the rear QR…
I do also make sure I put that tether strap is around the stay just in case the hitch were to fail, I do have to loop it round the stay once just to be sure there isn’t too much slack looking to get into the disc…
Not tried mounting it on an FS bike, but I can’t see it being too much of an issue. the hitch plate can rotate a little if needs be, and the sprung connector arrangement in the arm acts like a sort of UJ to account for plenty of jiggling and joggling (as my eldest calls it)…