Metagross doesn't get the STAB boost with explosion...
It does say BANDED OR STAB. Band explosion from metagross does (93.63% - 110.38%) to 252/252 bold, so I'd say it's a pretty solid way to get rid of it.
Also, here's a new set idea:
Reuniclus @ Leftovers
252 HP/252 Def/4 SpDef
Bold / Magic Guard
Psychic
Acid Armor
Recover
Calm Mind
Taunt bait, countered by other boosting Psychic types, hard countered by any Dark type, but one of the most tenacious setups I've ever seen/used. If your opponent doesn't have a boosting attacker that can stat up alongside this guy (or something like Gengar that can quickly hit its weaker special defense with STAB super effective hits), your opponent is finished. Trick can be spotted coming from a mile away, so pair this up with something fun like ScarfTar or other pursuiters like Drapion who can survive a Focus Blast and outspeed non-scarfed psychics/ghosts (in fact, Drapion is probably the single best thing to pair up with this set since it can provide Toxic Spikes support to beat out Sableye and Chansey/Blissey while having the bulk to tank hits from stuff like Gengar) Here's some calcs that show how awesome this thing is though, and all calcs are at +2 defense:
CB Scizor U-turn: (38.68% - 45.75%)
CBTar Crunch: (45.28% - 53.77%)
CB Escavalier Megahorn: (67.92% - 80.66%)
CB Rampardos Head Smash: (49.06% - 58.02%)
CB Haxorus Outrage (rivalry+): (45.28% - 53.30%)
CB Lickilicky Explosion: (51.65% - 60.85%)
These are the most powerful physical attacks in the game, and they can all be tanked and recovered off assuming that you don't get haxed, i.e.
Turn 1: You bring reuniclus in fresh off of a death, and your opponent switches out as you use Iron Defense.
Turn 2: They attack as you use Iron Defense again.
Turn 3: They futilely continue to attack as you Recover off the damage and then start to stat up with Calm Mind at +4 Def.