Well having done in excess of 22k curses myself on my pure, I can say it IS good training just it can become very tedious. You will miss 95% of the time if you wear full metal armour of any sort and if you do it, you only have to wait a few seconds until you can cast again. IMO the best place is the mage of zamorak under the stairs at Varrock castle. Have fun *raises eyebrows* :D