I was reading the newsletter about the RB333 and it’s fan control.
If it’s true that one fan sits idle until the main fan has issues as a suggestion it’s probably better to run both fans at 1/2 the speed needed by one fan so they wear evenly and you always know both fans are working. Not good if one fan fails and the other silently died or was DOA. When one does fail the other should crank up to full speed and a trap sent to notify the operator there’s an issue.