LOVE my Slidelock! Actually, I have two, but normally use the 14". Both have the "lighted edge" which isn't really lighted, but a tint that reflects light. When I cut yardage, I fold in half twice - once selvedge to selvedge, then again - so 4 layers thick. Cuts without a problem. I have also cut 8 layers... Not sure I'd recommend that, but I've done it. Keep in mind, you have to have a good blade in your cutter. The Slidelock prevents any slippage at all.
I was lucky enough to buy mine through a group buy; they are also available at quilt shows as listed on their website. Although I didn't pay the regular price, I honestly would say that if I had, it would STILL be worth it.
Sometimes I cut using the lines on my Martelli mat (the only mat that I've found to have reliable measurements), other times I use an acrylic ruler as is shown in the demo video. While working on Celtic Solstice, I found that the Slidelock is 3 1/2" wide, so didn't have to measure - just cut on both sides.
Maniacquilter - I thought I was the only one who didn't like the June Taylor ruler! Hated it so much I gave it away. I'm glad to know I wasn't the only one after all, lol.