As far as I know, the function and reliability of a circuit breaker
type GFCI and one installed elsewhere is the same. The main difference
is one installed as a breaker will protect all devices on that line,
while one installed elsewhere will protect the outlet it is installed
in plus anything connected downstream of it. When installing outlet
type ones, a single one is frequently used to protect multiple outlets
downstream.

To test it, just push the test button and it should trip.