Counting out loud and using a metronome serve different functions.
Counting out loud teaches you how to apply the right amount of time to each different
type of note.  The metronome helps you count without missing a beat.

It is true you can us a metronome to help you keep the rhythm steady, but
if you don’t continue your habit and knowledge of counting, you wont’ know how to
play a song, even with a metronome.  A metronome is an excellent tool to keep your

counting and playing steady.  I am sorry, but a metronome alone will not teach you how many beats to apply to a note.  You might think you are matching the beat to the metronome, but you might be matching the wrong notes to the wrong metronome beats if you don’t know how many counts to apply to your
notes.

I hope this makes sense.  ~smile~