Buff lasts a minute, or even longer if you have buff duration AA's. But more importantly it's limited to FIVE CASTS. Which I guess is a good thing since it would be hard to kill yourself with 5 casts, even if the spells burn up HPs at 600% the rate of the spells' mana cost.
On FV I saw someone offering this for 20million pp. Too much for me although I was thinking that any item of this sort, such as the manastone and the mana robe, historically have been in BIG demand and often sold for lots of plat. When the manastone was still dropping in P1999 the waiting list to kill the mob who drops it had a week wait. That means you had to be sitting at the camp spot for a week waiting for your turn!
I passed on the 20milpp ask price. Then ironically a couple of days later I was going thru my bank bags and found one I must have bought long ago and stored away. No way I paid anything like 20milpp for it, although I don't remember what I paid. Nonetheless, still a nice item to keep in your hunting bag. 5 extra spell casts at the end of a long quint-kite could make the difference between victory and defeat.
This is particularly useful for a druid, who could pop their Spirit of the Bear AA (temporary 50k HP buff) and not really suffer any base HP damage loss from casting these spells.
Edited, Dec 31st 2017 7:41am by Sippin