Like, being locked into something is pretty bad this metagame, yet without band azumarill hits with roughly the same as a base 100 atk pokemon, which some would say is pretty mediocre.
No, it doesn't. Huge Power doesn't double the Base Stat, it doubles the attack stat itself. So Max Attack Adamant Azumarill with Huge Power has an Attack stat of 436, which is just two points below that of Max Attack Adamant Groudon (Base 150 Attack). Without a Choice Band.
Anyway, Choice Band Azumarill is really useful if you put it with the correct team and don't attempt to play it like a bulky Water-type like Jellicent or something. CB Azu is, first and foremost, an offensive Pokémon. It's main purpose on the team should be to get in on something slow, weak, and/or paralyzed and either wipe it out or predict your opponent's switch-in and crush it with the correct coverage move or STAB. It's meant to be a tank buster. Yeah, it can tank some hits with its high Hp, good typing, and decent defenses, but it can't rely on that because it is slow and has no healing. Also, Azumarill hates the crap out of status, which is common, so you can't play it recklessly. If you're careful with Azumarill and use it to wear down the opposing team the way it's intended, it's a great addition to teams that rely on late-game cleaning.
Also, as I said before, relying on Azumarill's Aqua Jet for priority abuse is stupid and predictable. It's something you want to use carefully and sparingly. KillerDraco has the right idea when he says that bluffing it to force a switch and deal out a hard hit to the switch-in is a good tactic.
EDIT: Ninja'd by mc
ninjadanger, somewhat.
I disagree that Sub Azumarill is the better set. Frankly, it doesn't hit hard enough to justify using it over other Pokémon, even with its good coverage. Maybe I'm just not using it in the right context or teams, but I've had much more success with Choice Band variants than anything else.