I don't really know DnD's rules about that but being able to cast 2 level 1+ spell with metamagic looks really OP.
I can't imagine how powerfull the sorcerer will be at higher level compared to any other caster.

I think it would be better balanced if you could only use 1 spell + 1 cantrip (or eventually level 1 spell) per turn with this metamagic option.

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