I would say it depends on which Janome and which 1/4" foot you're asking about. I have the O2, Clearview, and Acufeed 1/4" feet for my 7700, and they're OK but I still have to move the needle quite a bit (prefer the clearview of the 3 unless I'm going over seams). For the Acufeed I actually have to move the needle to 6.1 to get 1/4" and then it's not quite as "scant" as I'd like it, but moving it any further to the right causes the thread to break.
I also have an Elna 760 (the same as the Janome 9900). I absolutely love it for piecing - it's 1/4" stitch with the 1/4" foot is exactly where I expect it to be without moving the needle and the feed is fantastic. I *think* that stitch and the awesome feed is the same on the Janome Skyline S5 and 15000 (maybe also on the 12000) as well. I really want to replace the 7700 with a machine that has the same piecing capability as the Elna but the larger throat of the 8900. Crossing fingers that Janome comes out with a larger harp version of the Skyline (don't need the embroidery capability of the 12000 or 15000).
Michelle