Mkotch

I have one that I bought from Deb herself. She recommended the yellow one as the most see-able. I also have the Fons and Porter ones which are clear. I actually like them better but I think it's because they have pointed ends that fit into the corners of the fabric you're drawing on. Actually, I don't use them most of the time. I draw one line corner to corner and use my quarter inch foot to sew along either side of the line. And sometimes I just cut the squares corner to corner and sew them together the old fashioned way. Do what works best for you.

Kitsie

I just use my Creative Grids ruler, place the 1/4" mark on the diagonal and mark each side of the "seam to be".

FWLover

i have Deb Tucker one but prefer the ruler described above. I like to mark in the center slits also so I can use scissors to cut.