I bought the June Tailor Shape Cutter Plus 18" X 24" size last month on Amazon.com and love how fast and accurate I can cut pieces now. About the only way you can goof is to mess up the mental math or mis-align your horizontal fold before cutting. I do make a little chart for myself if I have to make multiple widths or fractional strips. (for instance: 3.5, 7.0, 10.5, 12.0, 13.5, 15.5, 17.5 for 3.5", 2" and 1.5"). I write it on an index card and place it next to the mat. Once I did that I could cut up a yard of fabric in a hurry.
Of course you will probably need a 24" X 36" mat or larger to use the ruler. I like to flip it on the plain side for cutting strips. My Olfa mat is really old, I'm assuming they still are made with a plain side. The 60mm Olfa hand squeeze rotary cutter is what I like to use with a regular 6" X 24" ruler, but I found that it is a little harder to fit in the slot starting point on the June Tailor shape cutter than the 45mm. Now I need to save for the 45mm ergonomic rotary cutter.