In a previous saga, some players new to ArM had difficulties in adapting to multiple characters, and therefore always played their magi.
In my current saga I think we have very few companions, but grogs get used a lot. Players are careful in not sending their magi out all the time. But if they go adventuring, thay cant study or do labwork! I think things should even out over time.
But still I suggest ecouragnt players to design both a grog and a companion. Ideally, a companion who dislikes their magus, or has other interests. That way a player rarely has both magus and companion on the same adventure. When a story is introduced, players decide if their magi are sufficiently interested to go along, or is they want to play their companion instead, or a grog.
We have a House rule that any story must have at least two grogs along, so the grog-player isn't too alone. Grogs work better in groups, with the magi a bit distant, so they can trash-talk them
Also, encourage players to control 1-2 grogs of the ones brought along, even if playing a magus or companion. All character aren't necessarily active at the same time. Once you get to the place, magi want to sit down and think, or need to cast investigative magic. Grogs set up camp and go scouting. Parties quickly split up to do several things at once, so it's good to control several characters.
Being SG so much I don't have a companion, I think. I just play grogs if my maga does not attend.