The Linex is rather small actually: 115mm / 4˝" along the long edge. Also, mine is graduated in mm and 32nds, and the holes are on ⅛" centres. It comes into its own in combination with a T-square or, better, a drawing board with parallel motion.
Chris, I like your homemade ruling guide a lot, because it's simple, effective and tailored to your needs. If you could make one up in transparent plastic it should give good service for years, and might well be a better bet than the commercial alternatives.
*Edit* Eeek! I just noticed my mistake in the first sentence, which was a significant one. I said "short" when I meant "long". Now amended ... the template really is a dinky little thing.