I was considering a handfasting as a unity ceremony because I thought it would be meaningful for my FI, who is very interested in and connected to his Scottish heritage. I also come from Irish and Scottish background although it is not a huge part of my life.
I am a little concerned that it is too much connected with Pagan and Wiccan marriage ceremonies (and it did indeed originate in pre-Cristian days), although the majority of wording options to be read during the actual tying of cords is just unity-related and not religiously-specific. At least that's what I found when googling it.
There are also specifically Christian readings for handfasting available online, but I would rather skip it or do a different unity ceremony if it would be religiously insensitive or offensive to either Christian guests (the majority I think) or our guests of other varied religions.