I keep running around the forgotten reach, whacking rare critters but the number of keys that are dropping from these loot piñatas - to put it frankly - sucks.
Since we have to collect so many of these things it would be nice to have a drop rate that is more than 1 in 4.
Are you doing them solo? Try joining a rare farming group, or a war creche farming group. It goes a bit faster.
Burn off your element junk on those Dragonscale Expedition bags. You’ll be swimming in so many keys you’ll feel the urge to come to the forums and complain about it.
For anybody who’d like a visual reference. They often contain a chunk of dust and have a chance of a key.
Interesting… I’ll give it a try but I haven’t seen a key from the bags yet. Just more powder 
And now I’m looking at 1 in 4 bags = key. So let’s do a wee bit of math…
If each rare drops 500 powder and has a 1 in 4 chance for a key… and each bag costs 2k powder and has a 1 in 4 chance for a key… I only need 84 rares to get my 28 keys for the week.
Now, if I’m fair about this and I take a look at wowhead to determine the drop rate for these awful things… I can see most rares have a 50% rate. That would require only 48 rares to get all the keys for the week.
Assuming we can get 8 rares in 30 minutes… (yes, optimistic) and they continuously respawn… that’s 3 hours of just killing rares to get all the keys. Anecdotally … I’ve already gone past 4 hours of grinding this week and I haven’t even hit half the keys I need this week.
I guess RNG being RNG but maybe I need to stop playing a game that keeps me here with this sort of thing going on. Blizzard, please fix your drop rates on keys.
The bags for me, at one point, was one bag one key. Not too bad. Tried again later in the week, and it was 1 key per three bags. Not sure if it was stealth nerfed, but needless to say, I’m done w that zone.
Key farming isn’t fun.
I tried on an alt and got a better result of 3 out of 4 rares = keys… but I’ve moved on to other, non-wow, activities for my weekend now. I think I’m over key island now.
It’s called a day job! 
Get the other item that same vendor sells, and just loot the bazillion chests you’ll come across while doing rares.
There are dozens of those chests, they respawn, and each one is another shot at a key.
Also, the keys can be mailed between characters. If you have any level 70 alts do the vault introduction quest for an easy 6 keys and send them to your main.
My main concern is that to unlock the raid in 10.1 you have had to unlock 1500 Zskera vaults.
I you have 10,000 of the currency (5 bags) - you usually get 1-2 keys and 6000 or so currency back. So you can rinse and repeat.
I factored the currency into my estimate.
Unfortunately RNG makes this a per-character conundrum. My hunter did pretty well with rares - about 1 for 2. But my warrior is easily 1 in 4 and when I get really grumpy it is trending 1 in 5.
I’ve tried it out. It’s not fun. I won’t focus on farming keys to unlock vaults. It’s silly.
I had 60 keys after farming enough rares to deck my alt out in 395 catch-up gear. I got about 20 of them gambling on goodie bags.
What is the “vault for the week” thing? I’ve done it with 3 characters and maxed the ring on the first run through on each. I’m feeling pressured to run more alts through just to get rid of all these keys I haven’t been using
I’ve collected 30 keys in less than two hours just farming the bosses as they spawned.
They spawned so fast they often overlap. By the time I kill one you can most than likely go to the next one and find it half way dead.
I finally took the time to look up what the jewelry kit and hammer were all about. Now I have the three best gems in this hunters ring, and won’t be going back.
I still have my alt army to do, but it won’t take long to finish each of them up.
The devs missed a great opportunity to have the gift packages you get inside the vault with the neltharion coins give keys. When I turned in the first coin I thought for sure there would be keys but nope. Just grays that sell for silver and fruitcake. Or to be able to fish up keys in the fishing cauldron.
I finally finished the mount this week I’m not going back to the vault. Having to kill 1-6 rares for 1 key was a dismal drop rate .
Lol. I figured with my luck there was bound to be someone that got a key (or multiple) per boss kill. I mean it’s that or you’re just making stuff up at this point 
What’s the respawn rate on bosses? Once per 30? Per 60? Even if it’s once per 30 and you killed as they spawned and had a kill rate of 1 boss every 5 minutes you would still be at 2.5 hours for 30 keys assuming drop rate is 100% for you. And that’s a little too ideal to be believable.
Join a rare farm group on an alt who can use the sigils and books to upgrade trash gear to less trashy gear. Mail keys to main.