I have a WOA Varmint upper and love it.
While on a coyote hunt around New Years my friend I was hunting with had just switched out his conventional upper with a side charge upper, after using his gun for a day it made a side charge a must have for me. only problem with the swap is that you wont get the barrel nut off a WOA without buying a barrel nut tool from WOA for $39 it is unlike any other barrel nut.