doesnt seem to give alot of crystals it seems to be very random i had over 15 items and only got 5 crystals out of it

it just random or depends on rarity?

It depends on rarity. If you put in Rare items, you're guaranteed to get at least one crystal per item. Anything less than that has a chance of giving you a crystal, with normals seeming to have about a 33% chance and it going down from there. Conversely, if you put in a r90+ you have the chance of getting more than one crystal.

ok ty