Zap Pay is another one of those ideas which tried to fix the problem of having so many apps by adding another app to charge your car. So far it seems to be a total failure. As you said they don't support many networks, and the majority of chargepoints they do support already take a contactless credit card anyways.
Maybe it would be of more use if they worked with those networks who don't offer such simple payment methods.
I'm not at all interested in using apps, but if something like the Electric Juice RFID Card was to continue to grow and add all the major networks I would definitely use that over contactless for a few reasons:
-No contactless card usage limits before requiring a PIN entry
-No pre-auth transactions sitting on your bank account for up to a week holding funds and making it hard to keep track of spending
-All usage paid with one simple monthly direct debit
-Easier to get a copy of itemised usage so you can submit claims for charging expenses, if necessary.