Thank you all for the feedback. I had a look at the Slidelock Ruler, and I'm sure I've seen it at quilt shows, but never really paid it much attention. It does look like a very useful tool and will be on my backup plan list. My husband just rolled his eyes, as only this morning I was discussing wanting to get a Blocloc ruler, and now this ruler is recommended.
I'm going to give the twice folded method another shot for a bit and see if I can't get more comfortable with it as I mentioned in my earlier reply to RhondaK, i do seem to have a bit better result with it, having tried it again.