Im growing real tomato's not "Tomatoes" out of a topsy turvy and the thing is a fuckin beast!!!!! It seems to work well but it is very shady and I dunno how well it would work for marijuana unless you had somewhere in your yard to hang it like off a bird feeder pole where it would get 360 degrees of light. also the plant turns "U" shaped as it grows because the leaves begin to turn up to face the light. Mine is like a large squiggly shape now with a bunch of tomatos waiting to ripen on it! best $10 I ever spent. don't gotta worry about slugs or other critters touchin my shit.
Like Dr. G's topsy, most ppl can get the thing to grow, but will it ever outperform a right side up? NO.... It's just a fun thing to try and play around with.