Got my tank merc to bite the DT from the horsey, so I was able to live long enough to kill him and get the item last to finish this quest. I was a little saddened by one thing that I guess I didn't see listed here due to not wanting to read down 386 posts. The GOOD and the BAD are:
GOOD: It's insta cast/clicky. I love that part. Also, the haste is insanely fast. Ridiculously fast.
BAD: It only lasts like 25 seconds. So it has to be recast constantly. In order for it to work in fights ,you'd have to make a /doability hotkey for fighting that included this on a timer mode. Like /assist Tom /attack /Doability 1 and make 1 be a cycle of this being recast over and over on a /pause 10 cycle, etc.
I hope this helps. It's a good item, it stacks nicely. Just too short lived to be useful in day-to-day fights where you will forget to click it. The alacrity potion is only 2% slower for me in the end.
Just my 2cp