Mobile Spellcasting is in someways even better... you could move up to double your movement in a round and still cast a spell. The prereqs are absurdly low, too. You do have to be somewhat careful with the concentration checks, tho.
Flyby attack has the prerequisite of a fly speed, and if you're trying to pick it up on the basis of spells (fly, overland fly etc) giving you a fly speed, thats opening up a can of worms...