I would say it increases the surface area that _must be attacked_ rather than the surface area available for a single attack. So like, if you have a square they just have to attack the square but if you have a cube they have to attack six squares. And really the attack vector of primary concern, in my opinion, is the creation of the key and that math can be verified separately. Once the multisig wallet is made, the hardware doesn't matter that much going forward if you're not using the set up forfrequent spending. just a quick thought