I was assuming a flat "free" boost to their total revenue stream, so my assumption was even more generous than yours.
I sincerely doubt they were only 10% of revenue away from being solvent, even if it was money that came out of nowhere. Reports I've heard are that Fitbit paid ~40m to pay off Pebble's debts, meaning that instead of $10/yr the subscription fee would have to have been closer to $10/mo.
Whereas on the $43m they still had to manufacture, ship, hire designers, engineers, etc.
That $4m profit would be a LOT more than 10%, that would cover 20 people's salary