Yes, that works really well and whatnot. Totally reliable way of doing it. :P
Because the flatpak components/dependencies of a program can differ depending on the host (for example if you have an NVIDIA card, it will pull some NVIDIA dependencies), so if you export a program from a non-NVIDIA system to the other, it won’t be complete to work reliably on the new system, but the missing parts can be downloaded on the Internet, it’s still reducing the bandwidth requirement.