Double edged blades are outdated for modern military
applications. They are worthless as tools. They are more likely to
break. And you will never sharpen one as well as a single edged
blade. A double edged blade also limits your attack options.
Agreed about double-edged blades not being tools - I had my
Victorinox for that. Hell, that little 'nox happily
outperformed the other guys' Jungle kings and what not during
jungle survival.
However, i'd disagree with double-edge limiting your attack
options. Either way you hold it, you won't have to worry
about which edge cuts, and that expands your options. The
Fairbairn Sykes is primarily a stabbing instrument, but the Mark II
is much better at cutting IMHO.