We use a "no item above your level when the game starts" rule for char generation and I do not make Items more than 1 level above the PCs level available in the game. Under those circumstances they seem just perfect, as you can not buy a +2 weapon till you reach level 10. (+2 weapons being level 11 items)
Currently in possession of my players: A lesser Energy Resistance (fire) crystal and a lesser Life Leech Crystal. Both were found as loot, but I think they will buy some more, as they seem to like them.