We have used Waze and GoogleMaps -- often at the same time. Kinda like the guy who wears a belt and suspenders. My wife has one of the nav apps running and I have the other.

The phones are plugged into the car so we're not running batteries. Also we have T-Mobile as our carrier, and they are, near as I can tell, the most liberal carrier regarding data, etc. We've never ever had a problem with data charges. Also, we have Android phones.

As to why the two apps at the same time?? We find that, only very seldom, one stops working. It generally happens when we often take the non-toll roads (and have that choice on the phones). But we've been in the outreaches of Scotland, roaming the Italian countryside, or driving down a rocky road in a French vineyard -- and we've never gotten lost.

I've also noticed on the last couple of trips, the cars come with nav. We don't ask for it. And that's pretty nifty, too.