It's valuable in the sense of:
If an Arms Warrior was using one, and the proc went off; I wouldn't want to be the person he's targeting for the next 10 seconds.
Other than that, The Jackhammer has great burst value. But There are better weapons for over-all damage output. And until someone does a comparison of a BiS Arms Warrior using Jackhammer vs BiS 2H'er from a DMG Recount.
I'd say record the dmg 6 different times for both weapons.
3 times record it for 30 seconds, each recording with the jackhammer procing at least once for it's full duration.
3 times again, but for 5 minutes instead of 30 seconds.
Then average out the damage between the 30 seconds of the two weps and 5min recording of the two weps.
This will show each weapons dmg for it's burst value and the long-term dmg.
And this time, not with White hits. Using this rotation: Mortal Strike --> Overpower --> Slam ---> Repeat.
Until then, the only thing that we have actually confirmed is how often The Jackhammer procs while dual-wielding and only using white hits. 1 Proc Per Minute is what I believe was recorded. Not the best but definitely not the worst.
No one is saying that the Jackhammer is BiS@mrdooby, but you can't state that it's there's a better weapon since no one has recorded short-term dmg(with at least 1 proc from TJH) and long-term dmg. All you can safely state(without anyone arguing with you) that the Proc rate from the Jackhammer is not as great as we all hoped.
Maybe this next part will be more helpful to you
Ochimaru.
This item is so incredibly rare, that the value of the item is only determined by the buyer; not the seller. There hasn't been enough sells for this item to be even deemed a price. And not only that, the jackhammer still hasn't been tested enough to actually determine if the haste proc(in both short term and long term dmg recordings) can outweigh the overall better dmg from the current BiS 2her(that has yet to be tested against the Jackhammer).
Here's what has been confirmed:
Using white hits/Dual Wielding two of them. --The Jackhammer sits at ~1 Proc Per Minute. The Proc does not stack, it refreshes itself. The Proc chance has not been confirmed.
Until someone does test it on the PTR, we cannot assume the jackhammer is better than the current BiS 2h'er(vice versa) nor can we determine the exact price value. As mrdooby stated, his value of the Jackhammer is 20k at most; while the seller that I spoke to back in wotlk valued it at 250k.
Since no one can actually prove(or disapprove) if The Jackhammer is BiS with actual evidence to support it, there's not really a price on it other than the fact that the drop rate is so freaking low; that it's only real value is in it's rarity. And since the current BiS 2her is much easier to obtain than the Jackhammer, there's not really any point in someone wasting their time with the Jackhammer since the current weapon is getting the job done.
To make an analogy:
Comparing
Foreman's Leggings to
Kalecgos' Gift
Foreman's leggings takes quite a bit of RNG and can be very time consuming to farm. The next best thing has 6 less armor than foreman's and to obtain it; you just complete a short chain-quest. Just because Foreman is technically better, doesn't mean that it's worth a lot of gold. It's better, but kalecgos is easier to obtain and you only lose 6 armor in comparison. For trial accounts, they might not even waste their time farming them. For people buying them off the auction house, I would probably spend around 500-1000g at most for foreman's.
The Jackhammer may be MUCH BETTER, barely better, MUCH WORSE, or only barely worst than the current BiS 2her. But regardless of that, the current bis 2her is very easy to obtain. That being said, that alone puts the Jackhammer's value way down; especially since there hasn't been enough tests on the Jackhammer.
Given our current info on the Jackhammer, Mrdooby's number is much more accurate than the one I received back in wotlk. If we did more tests on the PTR, that number may go down to 15k if we confirm that it is not better than the current bis 2her; maybe even less. However it's very difficult to put a number on it if it ends up being better than the current BiS 2her. If it's barely better, well maybe no one wants to pay a gazzilion gold to get a weapon that's only barely better. So 20k may only go up to 25k at most. But if it is waaay better, then that's where the seller will make some big $$$. Given that it is already super rare and impossible to farm, if it's much better than the current 2Her; then the price of it could easily be equivalent to the Stam lens(back when it was GF'd in cata) or Unearthed Bands(w/ GF'd Stats) if not much much more.
Best of Luck to you.
EDIT:
I cannot think of one class where it would be BiS.
Yes it's proc is awesome. But you can wait for ages for it to proc and it likely won't proc when you need it...
If any class, it'll be a warrior. 50% Haste Increase for warriors as of 5.2, puts the haste proc over 75% haste increase for 10 seconds. But the downside is, you have absolutely no control over when the proc happens. If the proc happens when you need it, I'd hate to be that person getting hit(lul), but if it procs when you don't need it; it's just a wasted proc.
If someone can prove that the Jackhammer is better and we can determine the proc chance%, we could easily time this weapon with Lifeblood+Trinkets+RacialCDs(if any) for when we need to burst. Then Swap the weapon, after the 10 seconds are up, and just use the current bis 2her until your CDs are up again. It's very easy to assume the weapon is no where near better any other 2hers if the proc isn't up. So just use it for it's Haste Proc, then swap your weapon out after the 10 seconds are up
Some nasty burst.
