Well, it seems most people attracted to polyfi are in a bit of a place of fear. There's the obvious one about STIs and others that are really more control based.
Can/will you "adapt" ?
I guess that depends on how important restrictions (lack of) are to you. Some people really get a rash over restrictions they don't agree with and eventually it becomes a full break out. Others seem to be able to weigh pros and cons and be content if the pros seem to outweigh the cons.
You are you so only you will know.
It's quite likely though that the request is based on newness and it may well be that even the other couple will get more comfortable and rethink the restrictions they've put in their own life as well.
Probably no harm exploring for awhile. it will either work or not.