Think of this, a single edged isn't as efficient as a double edged sword. A single edged sword can only be used one way and needs to be turned to attack where as a double edged sword can utilise both edges of the sword so you can immediately change the direction of the swing with less effort than a single edged sword, and Durzo Blint uses weapons that take the lest effort to kill any resistance the quickest to conserve stamina. As he should be concentrating on that more so now as he has aged. Yes a double edged sword maybe dulled and heavier than a single edged sword because if it is to sharp it will chip or to light and will be likely to break and become less than useless but retribution is the Iures (The Staff of Law) and as stated in the books (not sure were, if at all can't remember) retribution can't be damaged by a normal (or magical?) sword so can be sharp enough to slice through armor and limbs and light enough to easily use without breaking. Thoughts?