You still pay the transfer fee with or without a gemmed transfer for one, second not only do you save coin for keeping that other 30% you save days/weeks/months of feeds that you would have to use to catch back up. Is it worth it? that's subjective to the player.

lets say 30k from a 100k transfer. with 9 feeds a day it'd take 34 days to make up that difference so the question to the player is 1k in gems worth saving 34 days of feeds.
with the current price structure of mounts and their stars I'd say no but it may seem worthwhile to someone else.