lilia and marr are great to have. Especially marr imo , but as our unregistered guest here said , it's better to cc iris first. That being said , garret is literally the worst gold possible in my opinion , and even leanne is a better tank then him. DOn't bother leveling him up , and especially don't invest aff in him since it's pointless......unless u somehow have extra (which i kinda doubt) and just want to see his scenes. But even then , u're better of keeping said items for a better unit. As for garet himself , u can keep it as awakening fodder i guess.

TLDR : pretty much what the previous post said.