My friend experimented with quite a few empty refillable carts and there is such a large difference between them. A lot of them don't have enough flow or big enough inlets to let a massive amount of dmt through. o2 vari-flow is hands down the best of the best that I tried. There may be others that are just as good or better but the o2 carts are so good I stopped looking anywhere else.What is the best cart to use for dmt? I bought a couple recently and they seem to clog really easily.