I don't see how an opne reed call, that has the reed in your mouth can, "freeze up"! When I saw the title to your thread, I assumed you were using enclosed reed calls.
So I guess you need to explain, how does an open reed call, that has the reed in your mouth, freeze up, unless your mouth is an ice maker!

If the call is in your pocket while walking, you then pull it out to use, put it in your warm mouth, blow warm spit and air through it, how does it freeze up?

If that's the case with the calls you mentioned, electronic is your only option, and you're right, the fox pro is a great choice!