The Slidelock really helps. I either use the Slidelock alone, or I place the Slidelock on top of the ruler I want to cut with. Either way, it helps.
I even use the Slidelock on my June Tailor mats. The mats in conjunction with the Slidelock allow me to cut more strips before having to re-square the edge. The June Tailor Shape Cut Pro is big enough to allow me to cut strips just from the one fold. When using it, I am usually just cutting one fabric at a time (2 layers) because it is harder for me to get 2 fabrics lined up exactly at the fold. The limitation of the JT Pro is that the slots are all 2.5" apart, but it is great for that strip width. I can cut 8 strips with the mat before having to re-position.