Haste isn't a great spell, even twinned by a sorcerer.

The moment the caster loses concentration, the recipients lose an entire turn. Even if the fight lasts a few turns and you manage to keep concentration, you're sacrificing a lot of action economy for that extra action. And if you do lose concentration, you're likely in a net negative for action economy.

At higher difficulties, it's even worse. The extra action only grants at most one attack (the extra action ignores the Extra Attack feature). And enemies are smart enough to do everything they can to pile damage on your caster until it drops.

It's not a bad spell, but it's not the gamechanger lots of people seem to think it is. Especially with items like haste potions and haste spore grenades, which can't be interrupted (though still need to be timed well).