I always run CS ambush garrote, mut is only five points less then ambush but does less damage, ill always pop rupture after coming out of subterfuge and I really don't have issues with energy but also having 150 energy from the set bonus helps a lot. But the main point is that Ambush in IMO is the better opener then mut, but seeing as mut procs blindside its very tempting.I know this is from a really long time ago
but the advantage of Mut over Ambush is a risk/reward type of thing.
Ambush itself does better dmg than Mut, but Mut can proc Dispatch and offers an extra chance to proc poisons, as well as (I believe) two chances to proc Seal Fate (only one crit will grant the extra cp if both hits crit).
The rng benefits of Mut over Ambush are significant, if you get lucky and have even one of Mut's rng factors proc it becomes MUCH more valuable than Ambush.