I have the Mercury.
I've tried the Amp 1 Iridium a couple of times in a store and I don't like it as much. It's a lot more aggressive which may be preferable if you are primarily a metal player, but I just prefer how the Mercury sounds and feels. The Mercury feels a lot like playing a nice Marshall style amp. Not too tight, not too loose.
For reference, my go to sounds are probably somewhere in the "all eras of Gary Moore" vein from blues to 80s hard rock. I do dabble in metal stuff but it's a bit more old school too. Think Iron Maiden, Metallica, Ozzy, Judas Priest etc rather than modern metal bands. The Amp 1 Mercury does all that stuff really nicely.