Justicar Trueheart's hero powers give you roughly the value of a 1 mana card. There isn't a card that just gives you 4 armor so it's a little hard to say, but I'd say this is about right. Take Shield Block, which is a little more than this plus a card draw. Appending "draw a card" to an existing effect is worth 2 mana (Shiv versus Moonfire, Novice Engineer versus Wisp, Hammer of Wrath versus Darkbomb), so Shield Block sans the draw would be worth 1 mana, and give you more or less the same effect as this.
FYI: This is the new MVP of Wallet Warrior, but that's not really because of the merits of Tank Up! compared to the other upgrades. More that Wallet Warrior tends to drag games on long enough that they can use their upgraded hero power a ridiculous number of times compared to other classes.
HEH, GREETINGS
ARMOR UP
ARMOR UP
I can take the hit
Welcome to the grand tournament
TANK UP
TANK UP
I'M OUT OF CARDS
tank up? more like rank up
Perfectly balanced!
indonesian pls
go play Overwatch!!!! paladin player
When this hero power is around , something is tanky ( hard-to-kill) ;)
The best Heroe Power
Most infuriating hero power in the game... unless you're the Warrior.
That's the Warcraft III human armor upgrade, tier 3. Awesome. :)

Justicar Trueheart's hero powers give you roughly the value of a 1 mana card. There isn't a card that just gives you 4 armor so it's a little hard to say, but I'd say this is about right. Take Shield Block, which is a little more than this plus a card draw. Appending "draw a card" to an existing effect is worth 2 mana (Shiv versus Moonfire, Novice Engineer versus Wisp, Hammer of Wrath versus Darkbomb), so Shield Block sans the draw would be worth 1 mana, and give you more or less the same effect as this.
FYI: This is the new MVP of Wallet Warrior, but that's not really because of the merits of Tank Up! compared to the other upgrades. More that Wallet Warrior tends to drag games on long enough that they can use their upgraded hero power a ridiculous number of times compared to other classes.
Wallet Warrior's new bae.