I only applied it a couple weeks ago so I can't comment on long-term effectiveness. So far the product does what it claims to. As for application, there are online videos that show the preferred method (spraying) with rolling or brushing to fill in gaps and smooth out puddles. I did everything with rolling and it was a little tough to keep enough product on the deck at one time. Spraying would have provided more even coverage. Speaking of which, their estimate for square footage was right on. 1 coat is enough for composite decking if you're able to apply it evenly and brush in the gaps. Note that it WILL darken your deck (I have a light Cedar which is now a medium Cedar).