Doing the same thing over and over again and expecting different outcome is a classic definition of insanity...or was it stupidity?! Well, this is exactly what I am doing with my Sailworks in-flight adjustable kit -putting it on my big boom every year and then taking it off after a couple of months. For at least 3 years in a row!
My problem is that I can't figure out if the benefits outweigh the downsides. And downsides are several-it takes longer to rig with it; it gets in my hands when doing maneuvers ; distracts me sometimes and the worst one : the boom feels less stiff and solid when its not outhauled to the max because the tail hangs loose on the strings. I hate loose booms!
Raising or lowering the boom 2-3" makes a bigger difference to my Retros, but I of course it's different with racing sails ...when racing-you don't have time to drop and adjust the hight of your boom Well I'm not racing so ... Also I think it makes a bigger difference to a stiff cambered sail that stays always full then to "elastic " non cambered sail that goes from flat to full when powered up.
So today I had a decent blasting session with my 7.5 at the Calumet park . I came in and I stared at it for 5 min and then I took it off again after having it on for a couple of months . I really don't feel much boost when releasing the outhaul and I don't want to bother with it any more. If someone wants it I am selling it.
What is your experience with adjustable outhauls?

I am not familiar with non-adjustable outhaul. Is it cam action lever that that tightens in one sweeping motion and stays put with a built-in detent? Who sells it?

I think that you got that wrong. I'm talking about the on the fly adjustable outhaul, like this one from Chinook:


Mine is simpler one from Sailworks, with a buckle instead of cleat:
www.sailworks.com/adjustable-outhaul

I'm asking 40$ for it and I'll include 2 "burger" pulleys that I've bought separately because they don't come with the Sailworks kit /don't know how much is shipping/. There's one important detail to consider before buying a outhaul kit though-does your boom support it?! Does it have the tail block with the 3 pulleys like in the picture?