I don't want to be THAT guy, but "Mexican Style" is a little offensive. No comment on the perk but be more conscious.
why?
I really hope you aren't serious. The offensive part is you are insinuating that all Mexicans shoot like gangsters (or uneducated imbeciles) and/or are gangsters (see previous parentheses). If this isn't true, why is shooting all of your ammo at once "Mexican" ? Just because Danny Trejo shoots like a madman in movies doesn't mean all Mexicans do.
Also, having a hotkey for reloading negates the purpose of autoreloading. The only way I could see something like what you are suggesting balanced is a reduction in hit chance for every shot landed or something like that. Besides the fact the firing an entire mag at once would be OP (think about M249s), it would make it neigh impossible to conserve ammo at all, and you would be stuck in place wherever & whenever you decided to shoot.