I do not have them but have seen them being used. I think they are great and much easier to measure and mark what ever you want on your quilts than to get the tape measure and pencil out. why not ask your quilt shop to show you how they work, then make up your own mind. Happy Quilting.

Have F and P, not used it as yet

I have had the longer one for a while and just remembered I had it - used on a HST and it worked great. It will get more of a work out from now on.

i have never heard of them till now i have always drawn the line and sew on either side using my sewing foot to measure the quarter seam

I own two and use them both, great tools when needed. I think that they are a bit narrow to use for a ruler. I feel uncomfortable using it with a rotary cutter.

I would not use it for rotary cutting. you could very easy cut yourself
if it moved. They are just good for measuring your seams.

Have had mine for a few years. I don't really use it much.

I think they marker wider then 1/4".

I have one and use it periolically but use my ruler more often.

I tried these, but found it easier and faster to just use an accurate seam allowance in the first place. I found that I didn't take the extra time to use them. And I got the same results w/o them. But, I know people that use them religiously.