What FDL was
Firebase Dynamic Links mixed several jobs
Firebase Dynamic Links could route people by device, fall back to the right store, and (with more setup) support deferred deep linking into an installed app. It was free and widely used in bios, email, ads, and print.
When Google turned it off, every old Dynamic Link broke. Enterprise MMPs advertise themselves as full replacements — which is right if you need deferred deep linking and install attribution, and overkill if you only need store routing.
