Many players use ultras, but mostly vs protoss. Hydra/lurk will own terran metal, it isn't mobile enough. Spider mines can be annoying in early game, but as soon as zerg gets overlord speed they are useless. Tank pushes are wasted because they are not mobile enough to destroy zerg expansions before he gets new ones. Cliff drops are good, but u should make M&M in addition to drops. BCs can be hard to counter as zerg, because he will have to tech to defilers or devourers. My point is, metal in TvZ can be countered far more easilly than M&M, because M&M is more mobile. I have seen some players who made metal in TvZ and won, but most have failed.