I have been using the 14-24 on my 5D3 for almost a year now and I love it, it's incredibly sharp wide open and the low distortion for such a wide field is incredible. Granted I don't need the autofocus because I shoot mosly timelapse with this lens.
The novoflex is the only adapter I've ever used so I can't speak for any of the other ones, the manual aperture tab works well, and you get pretty good as estimating where you're at after awhile.
What is your procedure? To set the manual aperture, do you need to count clicks, estimate how far to move the lever? How difficult is it to reach - can you easily move the lever from behind the camera or do you need to be facing the camera?