you can steer 24 hours a day too, but few of us do that, we have autopilots. I have serious doubts that a cruising couple can keep an effective and alert watch for more than 24 hours or so. Even on fully crewed boats stuff get missed all the time ("did anyone see than ship RIGHT THERE??!!"). As has already been said, it is a matter of cost sensitivity, risk sensitivity, gadget sensitivity; and what may be right and good for one may not be right and good for all.

But I think the absolute bottom of the list would be a radar reflector, which ALL tests show are ineffective, and could instill a false sense of visibility to others. Much better to save that money and invest in a supply of NoDoze pills, if your strategy depends on keeping a good lookout.