Their juices are quite good for refilling cartos of the same flavor. Currently the 5ml and 30ml are exactly the same formula as the cartos, but the 20ml are not. That is something they are working on, as well as expanding the selection of juices.
A couple other
juice vendors I can personally recommend (for filling blank cartos) are Tasty Vapor and Ms. T's Bakery Essentials - really outstanding flavors and great service. Tasty Vapor has doublers (essentially 0mg nicotine
juice in the same flavors as his other
juice) that can be used to dilute the e-juice without losing flavor, and make it quite economical. A great option if you don't want to make your own juices from scratch.