Not OP, but part of the problem here is the "non-commercial use" restriction was a retroactive change to their terms of service. Their free plan previously had no such restriction.

On November 4, they emailed free plan users describing an "Upcoming Change to UptimeRobot Free Plan ToS" which somehow already took effect on November 1.

They aren't actually enforcing the change until December 1, but even then, that's still less than a month of notice. Even for non-commercial purposes, I wouldn't trust this service after this move.