Well as far as GF summoning goes, it's slow and pretty much completely unneccessary. Using them to kill anything like Ultima would take so long I can't imagine. Plus Renzokuken and other limits are far more efficient.
The End is really not something you wanna rely on IMO, it's cheap, and unless you want to waste good cards and items to become invincible it's not very reliable. Even if you do use them it's still a fairly risky tactic. A decent stock of curative magic and good defensive junctioning is a much better and less wasteful method of keeping your characters on their feet.
Splitting GF amongst more than three people means your missing out on a lot of junctioning and abilities. Getting a good team on disc 3 takes a hell of a long time if you want to build up every character and GF separately and without the aid of a lot of junction and stat bonuses.
