Yea they do but I can make a 5 gal can. I guess my question is whats the advantage of having that hole 3 inches up vs the ones at the bottom? I understand its a resevoir but would't it be a resevoir of waste water that already went through the medium? Basically wouldn't it be water you would otherwise want to have run off?
Well the idea is your medium has very good drainage, generally more than if you had the holes in the bottom. The point of the res instead of it being run off, is the water in the res is very highly oxygenated due to the cascading motion of the water through the medium (waterfall effect) and roots love this, it allows them to take up a lot more nutrient solution.
It's like in DWC, when your plants are in the net pots, they grow quite slowly but as soon as the roots hit the res the plants take off and grow ridiculously fast, Hempy has a similar effect it just takes longer for the roots to get into the res.
How big of a plant can you really grow in a 2 liter bottle though? they also kinda fall over pretty easy.
How does Hempy fit into a commercial environment?
Well it depends on the method, I use a Screen of Green XD and the screen supports the massive amount of growth I have. If doing a single cola, yes they are prone to toppling over
In answer to your second question, hempy is the lowest maintenance passive hydro system you will probably ever find... with large enough pots they can go a good long time without being watered so less work looking after them. You can also add a drip line to them and have a 24 hour drip which will give some even more amazing results! This way all you need do is change the res once a week and that is absolutely everything as far as looking after them goes (aside from the usual visual health checks etc in any method)
So it has it's commercial benefits in the low maintenance, high yield area and cheap setup cost, but if your seriously looking for properly commercial yields etc, like WattSaver said Aero or DWC will probably give you a bit more BUT in my opinion I reckon the start up cost of an Aero or DWC system, though it will produce more bud, the bud to cost ratio and probably the highest profit margin after expenditure would be in Hempy's just 'cause they only cost like £4 a bucket.
Probably just repeated a bunch of stuff WattSaver said but all in all aside from the potential commercial benefits I agree
Here's my 10l Hempy ScrOG from my last grow for you


A touch over 3oz dried and cured from 1 plant under 250w of CFL!
Enjoi, and Stay Frosty!!