Can you elaborate on the con guys. The stiffness when setting up? What the lines are hard to unroll from your bar?
And I assume the response on big kites gives you a quicker turning kite. ??
Not at all. They unroll from your bar differently. IMHO easier, they don't tangle so easy as traditional lines do. Q lines are just a bit stiffer. Hard to find a comparison. Let me try this: Imagine a five inch piece of line. You can hold that line straight, like an antenna. On the other hand you can do everything with it, bend it, knot it, kink it ... It will stay the way you left it.
The line has some sort of carbon core and is sleeved into a woven synthetic material.
Once wet they are more flexible. But still a bit stiffer than traditional carbon lines. Therefor they don't tangle so easy. If you manage to get a spaghetti ball, I think they are easier to untie.
These lines are so dense, that you'll have instant contact to your kite. No stretching, no delay, rather the aerodynamic twist of your kite. You pull, the kite twists and turns ...
Some say they don't stretch at all, some do a one time stretch before going on the water. I don't. In five years all my Q's still have the same length.
The lines are thinner than regular carbon lines. So they whistle in the wind. Some find this annoying while I love it. The moment they whistle I know I have the right wind speed.
They float (sorta'). I use yellow lines so I can see them in the water and won't get entangled.
Bottom line: I use traditional lines for my smaller kites (8 & 9m Naish) and the Q's on my 13m.