I am thinking of booking an Allegiant air flight, it is the only non stop available and will save a few hours. I am looking 5 weeks out and the plane currently has about 6 seats booked. So I anticipate the flight will be about 50% capacity. So rather than pay a fee for seat selection I am wondering if I can just move to an empty row after boarding. Does anyone have any experience with moving seats on Allegiant. Do the flight attendants have anyway to know or even care, or is this a protected revenue stream where the FA is expected to enforce seat assignments?

On legacy carriers I often board last and then just pick an empty row on flights with a low passenger load.