We only use Flagship varnish after trying many other brands, Rustoleum and Helmsman. We do use Helmsman on the inside of the hatches and other more sheltered locations.
We love Flagship ... so far it's held up better than the Cetol I used for years. Of course, I started with 10 coats not including the first two thinned "starter" coats.
But six months and three months out in the salty sea and Exumas, I want to add 2 more coats just to make sure it doesn't break down over the summer while we're gone.
Cheers! Jan