Frozen Heart on champs who don't use mana.

It gives 100 armor, 20% cdr and 400 mana and its passive reduces attack speed in an AOE. I would love to buy this on manaless champs like Renekton, Shyvana and Mundo. 100 armor and 20% cdr are strong stats for a tank. Would it still be worth it even if you don't use mana?