"Double-edged sword" has never worked for me, as a cliche. Do you often find yourself inadvertently smacking against the dull side of a single-edged sword, such that you stay away from double-edged swords for your own safety? rm is like a double-ended knife, i.e.: http://image.shutterstock.com/display_pic_with_logo/4253/425...
(Fun fact: many knife throwers grip the blade end anyway, rendering the cliche to an even simpler "rm is like a knife".)