For all tanking classes but druids it depends on the fight based on how much damage is unmitigable and depending on if you need a cooldown at your disposal. For druids though because of stam scaling I believe that the Black Heart would be on top especially considering its proc. The proc which has a 15% uptime and 7,058 armor gives you more than half armor of the Glyph if you don't consider randomness.
If he needs to ask about DMC:G as a tank trinket, he probably won't know when it works and when it doesn't. For those situations, having them use either black heart + Jug or Glyph+Jug is the simplest way to go.
Which is why they suggested it's a great DPS trinket.
But to the OP, if you are trying to purchase it on AH, I would not. But if you are close to getting it by virtue of inscriptions, congratulations, it's a valuable trinket to ferals, but my recommendation to you is to keep it for kitty spec.