Kunovski: it's just a thingie all backers would (did) receive, and so to make that available to non-backers (while still maintaining some exclusivity for backers) they packed it together with some other small stuff and will provided it to "completionists" :) you definitely don't need it, but the OST is nice and those Trunks are sometimes funny, so why not?
F1ach: Yeah maybe, I haven't used them this play through, on my first I equipped them for awhile, but took them off a short while later, I just didn't see the point of them, I didn't hear any talking that I recall, but the NPC spam may have drowned it out or made it seem just part of the background NPC drone....*shrugs* :)
yep, they're not that chatty :) I'm not far in the game but only heard them so far when the character wearing them does some extensive stealing, it says something like "if the other students in hunter academy could see you they'd be so impressed right now" ;) so it's basically these cheesy one-liners... the grail is not useful, just silly ;), but the OST is pretty great (though it only contains like 25 % of the game's music - see
this to learn how to obtain the whole music score legally, from your game copy)