70-30 is 70-30 no matter the shape. the reason some don't like to use the rectangular bars is that they are harder to apply due to the extra heat needed to melt them. [the bars are thicker]. I found that the best way to use the bars is in a mush pot. [do you know what that is??]. For hand application I always use the solder in wire form. I have a friend that buys the bars and halves them with a shear to make them easier to use.