Level
1st
Casting Time
1 Action
Range/Area
Touch
Components
V, S, M *
Duration
8 Hours
School
Abjuration
Attack/Save
None
Damage/Effect
Buff (...)
You touch a willing creature who isn’t wearing armor. Until the spell ends, the target’s base AC becomes 13 plus its Dexterity modifier. The spell ends early if the target dons armor.
* - (a piece of cured leather)
Does using a shield add to your AC bonus and/or end the spell early?
So the main difference is just not being able to dismiss the spell at will as an action? Oh and it's available for wizards twice
You have to have Shield Armour Training to gain the benefits from a shield and it does fall under the armour section in the 2024 PHB so I would sadly say that it will end this spell early yes.
Page 219
“anyone can don armor or hold a shield” (need training)
On same page “wear one suit of armor or wield only One shield at a time”
seems to still work with mage armor (shield) if proficient
The spell also says that 'The spell ends early if the target dons armor.' and to me the rules are saying that a shield is armor so it would end if you were to don the shield.
I am not a fan of it and I may allow a shield and mage armor at my table but if you are doing 2024 RAW then no.