I looked at the option and it was a no-fly pretty soon. A folder provides more constraints than a regular bike - it must fold small, be light and withstand all kinds of banging up. This kind of mount builds up an extended structure that is heavy if out of steel and else needs to be bulky to be strong if out of alu. In either case it takes unnecessary space by the seat tube. In addition you are going to be stuck with one outer ring size. My practical experience was trying out such a steel mount and it was a complete mismatch - beasts from different animal worlds.