I have the single line which seems ok, but in hind sight, I probally would have been better off with the double. Nothing wrong with the single, but unless you keep it on the tarp and in a snakeskin, a single line tarp ridge will tangle easily. I do love the way I can slide my rainfly along the single line to center it on my Clark. But then again, I'll probally end up hating it if the prussick knots jam up and won't slide. Knock on hammock--so far so good.
I would go with a double line and a snakeskin to keep things simple. If your good with knots you could make your own prussick sliding knots rather than purchasing a setup.
The only real advantage of the single line as compaired to a double, it really works well with very high winds and extra support for snow/ ice loads.
Some guys n gals use whoopie slings on each end of the rain fly.