There are
three
different e-cig models that use cartomizers: Kr8, E9 (and its little brother, E8), and GreenCig (not to be confused with Green Smoke, which is an E9). The most popular here on ECF is the Kr8, to which my following comments apply.
I have gotten both great and mediocre cartomizers (filled) from each of several suppliers represented here on ECF. [I've not tried the empty cartomizers.] Overall, China manufacturers don't have the best quality control: batches vary and individual carts within batches vary. Same goes with atomizers (and
batteries) of other e-cig models.
The best are probably the recently revamped cartomizers starting to appear. For example, I've read positive things about Vapor4Life's "Premium Cartomizers" and the new line (label unknown) of Nebula cartomizers about to be released by VaporNine. I expect others will follow (and may already be here, but I've not yet discovered them).