Doesn't seem like the trox's vestigial arms can do much. Sure they can hold extra items, but the clause saying you can't use them really limits your options. To move a held item from one of your vestigial hands to one of your main hands, where you can use it, you still need to spend an action, so what exactly is this race trait doing for you?
There are magic items like the Shadow Orb that must be held but not activated to function. There may be other items.
You could also hold an object while holding/attacking with a two hand weapon that round, then have the option to free action release swift action grab/change grip and then activate when you need it. Or hold two items in vestigial arms, one hand a weapon, and you have two swift action grab options if you need to activate one.