I find it easy to get a perfect 1/4" on my 440 (5.5mm) It takes more effort with my 820 (9mm). But other quilters say they have no trouble at all, so you have to try it for yourself. Of course, test drive your final candidates for purchase with the fabrics, threads, and needles you prefer. Bring blocks to piece, mini quilt sandwiches to quilt, and anything else you typically do, the more challenging, then better.