Frank: Rav Elyashiv, Rav Shternbuch and other gedolei poskim ruled that the prenups cause a Get Me’usa, for exactly the reason you mention, and as such may not be used.
And they’re virtually unheard of and unused in Chareidi weddings. (Chareidim are three quarters of the Orthodox community.) It is almost exclusively an MO thing, and even by the MO it is a minority that actually use them.