each of the rulers offers a different selection of radius sizes.
it looks as though they are also designed to achieve different types of patches/blocks that involve curves.
unless you plan to do a lot of curved piecing in the future i wouldn't recommend either one.
to make rounded corners, all you really need is a round plate, a CD or DVD, or anything round that you can line up to the corners. just make sure it's the size you want and is hard enough to run a rotary cutter around.
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- necessity is the mother of invention. lazy is the crazy aunt.
