Gear Carrier vs Gear Adapter

[MonsterAir]

Is one better then the other? Here is a link to what I am talking about. The top right and left pic-


http://rc-car-online.de/shop/index.php?r=&s=44t+spur+gear&x=0&y=0&lang=en&page=suche

 

[PegLeg]

One seems to be smaller/lighter. Less rotating mass = better. Will it be strong enough though? Keep in mind, some FG gear carriers won't hold certain gears. You have to match up the gear to the carrier.