i will still have the stat to sell using the 199dia one - the same one i would have using the 40dia one.
nope, the 199dia stone works like the cleaning stones we already know - except only for ONE stat of our choice, it gets deleted, you dont get the stat back.
yeah youre free to spend your dias on whatever way you like, still it does not make any logical nor economical sense for me , sorry

id rather keep some of the cheaper ones even if they use more space to use them more efficiently later ...
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RoMage:
untested, but its supposed to be this way:
you get a manastone of the tier based on the item you extract from. so if you extract from an item which would become a t5 manastone you can extract a crimson stat to t5. You wont get 6x T8 Manastones for extracting from a T8 statted item
So if the "something" you statted is a lvl68+ purple item and you statted it to t6 and extract a stat you will get a t5 stone with that stat. if you extract from lets say a raksha item youll get a t4 stone.
If you extract it from higher tiered gear the gear will keep its tier just like with using the cleaning stone we all alredy know. So if you want to put in another stat for the extracted one you'd need 3 manastones of the items' tier ... with the one usable stat on top of the stat list if you use crap-t5s).
So, to make it short:
what im going to use the random extractor for is:
- extract stats from drops or memento items that become t5 => more crap t5s for cheap.
- sell CLEAN items instead of crapped items , or make a clean t5 out of the so-cleaned item if noone wants to buy it

=> have a stat/or crap-t5 AND a clean t5 out of one item.
- extract ALL stats from pieces i want to re-gear instead of cleaning them ... i can pick the stats from the stones i want to use again AND can sell those i dont need anymore.
Example: Cleaning wings? never again, ill extract everything and sell the stats i dont need anymore.
im still using crimson+bunker sta/pdef , so with my current wings id extract all 6 stats, keep the 2 i need, add 4 new stats, sell the 4 old stats. instead of using a cleaner for 199 diamonds and wiping off ALL old stats and need to pull/buy new crimson/bunker stats...
what im going to use the 199 dia "REMOVE ONE STAT"-Stone for is:
-absolutely nothing
what im going to use the Attribute Purifing Stone (the well known old cleaner for wiping the complete item) for is:
- well ..... dunno lol. maybe cleaning gear completely that i want to re-use but has no stats worth keeping or selling anymore?
Short: WTB billions of 39 dia extractors and a whole lot of storage space.
But as you can see from the discussion with scootermtb, thats just MY use-case. Everyone may have a different one ;-)