i'm going crazy looking for one, too! they can check the resistance of the carto/atty without burning the coil, which is great if you're like me and have a pile of cartos and don't know the resistance...and also, if you want to test your own wraps. it's the most hard to find $20 accessory in the vaping world, it would seem. if anybody can find it, please let me know!
thanks!