I have the large single blade Agbay and I love it. I didn't think too big would ever be a problem, and I didn't want to regret not getting a bigger one when that large cake came up. The smaller one may measure 12", but it won't level a 12" cake, because of the sawing motion needed, so that's pretty limiting. I have also found that I like to level in from the sides to the center sometimes to avoid knocking off edges and or cutting fingers. The larger blade allows you to come in at an angle and to come at those bigger sheet cakes from all sides. I have never tried the double blade and can't compare, but I have also never wished I had it. It is so easy to cut and adjust, 2 cuts is not a big deal. I figured I could get the double blade if I wanted it, but never have. HTH
I just looked at the website - It looks like adding on the double blade after the fact, only costs $5 more plus extra shipping possibly over buying it up front. (for the larger one) So not much to lose by waiting if you are not sure.
Edited by yortma - 3/8/13 at 4:21pm