that is a great idea to wait if you have any hesitations. as you mentioned, this type of mount will only be useful for flush forward facing views. if you need ANY angle, this is not the mount for you. and as there are quite a few options on windows these days, I think that having dual payne windows may inhibit this mounts abilities to stop light reflection from inside of the home as they would merely reflect off the further panel of glass. just a couple of things to keep in mind.
and these also appear to be a set it and forget it type of mount. once you stick them, that’s were they shall stay. and I don’t see anywhere that they intend to sell more adhesives that would make it more mobile.