In upgrading our electrical we have the choice of either keeping the
main breaker inside the house or locating it outside as part of a
combo unit with the meter?
[Note we need a separate main breaker since the main panel is about 20
feet away from where the meter is and the supply enters the house]

Locating the main breaker outside would save a little money since we
avoid the need for a separate breaker box inside.

Are there any disadvantages (or advantages) to having the main breaker
outside?

(note we still will be able to shut off power inside at the main
panel, I assume)