Well having also invested in a number of 14x12s I'm going to stick with them but I'm not as sold on them, compared to double brood, as I perhaps once was. As with everything in beekeeping its a compromise of some convenience for slightly less flexibility. It is though pretty straightforward to go from a national to 14x12 even if you just drop the frames in and deal with the resulting comb while you switch the frames. I honestly can't remember how I switched mine over.