I have used Brightside to paint coachroof on our prior boat. Being a one part paint it is very easy to apply and the results are very good. As with any paint, the preparation/primer underneath is really important, as is the application of a not too thick top coat. I found the paint lasted about 10 years before it began to show serious degredation. Over that time we had our boat in San Francisco for 3 years and Marion (New England) for the rest. While in New England the boat is covered from November to May.
After 10 years, I had to sand down the old coat, reprime and repaint. I used a brush and did not spray. One part paint is easy to apply, but is limited in life span. Having said that, I have no relevant comparison of 2 part paint.
I have also used a Petit 1 part paint to paint the interior of our previous boat. The boat had Teak patterned formica on the bulkheads (classic 1965), and after vigorous sanding, 2 coats of sanded primer, and 2 coats of the Petit top coat, it looked great. Now, the UV degredation was not a problem, but the wear and tear of living on a 32 footer gave it some challenges, After 14 years, the Petit 1 part paint looked as good as the day it was applied.
I would think both the Brightside and Petit paints would have about the same life span. Now, Interlux and Petit may choose to argue that point, but they are allowed their points of view.
Doug