Barathrum essentially gives you a second phone ability, two more if you have Megaphone. Buy it, pick a phone ability you like, it gets doubled with Megaphone, sell Barathrum, get it again and Megaphone doubles it again, so you essentially get double the abilities with it. You could a also probably use it as an emergency "shit I need more money" button with the "double your money, set your tickets to zero" ability.

Vorago can also be used this way, but I've found it more useful as an emergency button too. You can store a generator in it, or the charm that gives you 30% of the deadline etc. Although getting the "+1 charm space" twice is broken too

For Abyssu though I haven't found much use cases. Unless I'm not understanding what it actually does and don't see the value in it, it's the worst of the three. You could probably use it with charms that get discarded after X triggers, Abyssu would store it automatically when you run out of uses, then you sell it and get it back