Thanks Time2tic,
Your point on the cumulative effects of nitrogen are well made as are the points on back-up.
When I go diving I'm usually on holidays, so I try to fit in as much as I can. This means I have to be wary about the dives before I fly out.
As you wrote, just with a trying to calculate and log dives on the boat, as would be the case with just a watch. I don't think so. And it intereferes with the beer drinking time afterwards...
But for dive-a day recreational dives without deco, I think they're workable. Not ideal, of course.