I don't really see what these Talents are good for. My first thought was deflecting a grenade, but the talents require a full action. I don't really see much use for them since they can only grab unsecured objects (so you cant' steal someone's weapon) and take a full turn to use (so you can't do anything as a reaction)

Mildly useful for some roleplaying circumstances, I guess, but not enough to make the talents worthwhile. Am I missing something? Is there anything useful to do with these talents?

Yeah; there are hundreds of things this can be used for by an imaginative player, just as telekenetics are a psyker's best friend. Although most of the applications are outside combat and niche there are times when this ability is likely to be a real party-savers.

If you just want to use it in combat, it's poor. But that's not what it is really for.