is it worth the gold?

it is against the right opponenet, like mundo and say volibear

A must against any healer, including carries like trynda with lifesteal

your mommy is worth the gold

when the enemy team is; volibear, fiora, elise, or something similar; yes.

it works pretty well against; Xin, anyone with a lot of lifesteal in their build, Mundo, Volibear, Singed(that ulty + FoN does a lot of regen), pretty much all ADCs, and anyone that has a BoRK

It feels very strong coupled with Frozen Heart, Randuin's Omen, Thornmail, and/or Frozen Mallet.

It's great on Jarvan and GP.

IT singlehandedly and significantly mitigates the viability of Mundo, Swain, and arguably Vladimir, for 2k gold

does your opponent have lots of lifesteal? (AD carries, etc)
does your opponent have tons of innate healing? (mundo, swain, vlad, etc)
do they have soraka or heal summoner?

if you answered yes to any of the above, grab it. it's worth it.

AD Sion will eat you alive. Get this, and he's managable.