Makes more sense to install spray rails inside the tubes (like stinkbuds aero system, aeroflo, etc), than top feed tubes up top.
Smaller plants will work ok in a round pipe system, but cannabis will probably clog it, even if its 4 inch or more. Like stated above, you won't get the film your looking for, just o2 starved roots.. which isn't a big of deal for lettuce or something.
5x5 fence post sleeves are better (with or without sprayers), but $40 a piece right now in my area. Even the 4x4 sleeves are like 26 bucks.
I Would probably just use plastic tubs with sprayers inside instead of doing aero NFT channels with costly vinyl post sleeves, if making a low pressure aero type of system right now.
I wouldn't use a standard NFT system to grow cannabis at all, really. But if you do, your probably better off building a long and wide table, with a pond liner or something.