There is indeed plenty of discussion here on these! Some people love 'em, some don't...
I started using these last season and would never go back to a 'standard' tapered leader.
I can't really vouch for their usefulness for anything over a 4wt but I found a huge improvement in delicacy and turnover when fishing light.
I would imagine that their aerodynamic characteristics would have very little effect on distance. It's also worth bearing in mind that they are 100% memory free unlike all the mono/poly leaders that I was using.
I got mine through Spider Plus (our very own Phil Holding):-
North Country Spider Fishing Flies
Customer service second to none!
Andy