"Flurry lessens your damage per hit by roughly 25%, it also increases your attack rate by roughly 25%, and it lasts for about 5 seconds. The net effect over that time is an increase to your overall damage.
Say you use a swod. Normally you'll swing once every 1.33 seconds. With Flurry you'll swing roughly every 1 second. Rather than being able to land about 3 blows in 5 seconds, you'll land 5. Rather than doing your full damage three times, you'll do 75% of your damage 5 times. 300% vs. 375%. So, it's actually about a 20% increase to your damage for the duration over the skill.
"
Let us break down Rex's assumptions here.
(In first paragraph he assumes 25% attack increase. in second paragraph he suddenly say it is a 66% speed increase, but never mind that

ASSUMPTION 1:
125% hit speed x 75% damage = 5/4 x 3/4 = 15/16 = less damage done
ASSUMPTION 2:
133% hit speed x 75% damage = 4/3 x 3/4 = 1. same damage.
Still not satisfying in itself!
ASSUMPTION 3:
150% hit speed x 75% damage = 6/4 x 3/4 = 18/16 = 9/8 = 110%ish
Now we are getting somewhere. The Adrenaline skills add maybe 2-3 DPS? While we at "ASSUMPTION 3" add 10% of a 20-25 DPS?? = 2 DPS.
However, still not very much. However it stacks with Conjure*
Okay, how can we pick the right ASSUMPTION from above? Well, while we wait for the BWE where we can time it, we can look at it the other way around:
Flurry, adding 1 hit extra in 5 seconds, will enable
- 11 damage from 1 conjure hit, at 10 skill
- 20 melee damage, average, with a great sword? (you tell me)
= 31 net extra damage for 5 mana
Flurry, adding 2 hits extra in 5 seconds, will enable
- 22 damage from 1 conjure hit, at 10 skill
- 40 melee damage, average, with a great sword? (you tell me)
= 62 net extra damage for 5 mana
Which is way too good.
Above would indicate that Flurry only adds 1 hit extra per 5 seconds.
So, what does that mean: It means from above (ASSUMPTION 1, less damage; ASSUMPTION 2, same damage) that Flurry HAS NO DAMAGE VALUE IF USED ALONE, IF YOU DO NOT USE CONJURE OR SIMILAR SKILLS.
It will however add to adrenaline regeneration.
Let us compare it with Hundred blades:
1 extra hit, 50% more damage, to each and every foe around you. It is much better. However, it has a 8 second recycle, which should not be forgotten. But it is far less mana intensive.
So the bottom line is
- FLURRY HAS NO VALUE FOR EXTRA DAMAGE, IF NOT USED WITH CONJURE * OR SIMILAR SKILLS. (This based on an assumed 75% damage dealt per hit, mind you!!)
- FLURRY WILL ONLY ADD 1 CONJURE BONUS IN 5 SECONDS = approx 2 DPS. IT IS NOT A VERY POWERFUL SKILL, EVEN WITH CONJURE, FOR DAMAGE CONSIDERATIONS ALONE.
- FLURRY WILL INCREASE YOUR ADRENALINE REGENERATION BY 25%; WHICH IS VERY GOOD, BUT AT A COST OF 1 MANA/SECOND.