So, let me start by saying that I know and use both of these tricks. Both are on me, prepped, all the time (I 100% of the time have a deck on me).
They are *similar* but also have different strengths. In contact, people can "see" the change happen, which is nice, but the order of events in FK leaves people more baffled.
Also, Contact is based entirely around a gimmick, and FK can be done with any deck and some spares. They require the same amount of prep, but FK is more examine-able and cleaner once cards are in mouths.
So, while I see where you're coming from - Contact and FK both are signed transpos, but they both have different strengths and different ideal situations.
Why not learn both?