Yes from me, Cloak of Oman feels more like a crowning gift for casters or archers, which don't really benefit that much from invisibility.
For assassins it's much more thematically proper to get Brannalbin's instead of Oman's.

Considering that invisibility from items makes your good consumption skyrocket i'm against such thing. I'd rather have Oman's.

Also, teleporting into closed rooms into positions the target previously though of as secure is extremely practical for an assassin.

How about making both crowning gifts ("cloak and dagger," anyone)? Far Slayer and Death's Blade are both kind of strange as Assassin gifts.

I'd understand far slayer but Death's blade? A huge two-handed claymore for an assassin that relies on subtlety and stealth? I don't think so.
Since assassins already have nice slaying weapons as potential crowning gifts, including some of the best in the game, the other slots should be different than weapons - I'd replace Death's Blade with Brannalbin's cloak of defense.
That leaves us with Farslayer which I suppose could stay untouched. There's already a bunch of nice things available for crowning and Farslayer would be difficult to replace with something that makes sense.
It's thematically more or less proper, though a big-ass crossbow like this doesn't inspire "remain silent, hide and shoot" and instead invokes the feeling of "let's go in guns blazing".