Number one-they’re not very portable. As described, they don’t fold and as such, they’re best used in a permanent studio.
Number two-they’re not as adjustable as most C-Stands. Although you can put longer upper stems in them for added height, there’s a certain point where they’re just plain going to become unstable and the usable range of height might limit you in some setups. (the maximum height you can use in your studio is of course determined by your ceiling height , minus 1/2 the distance of any soft box you might hang on the stand.) I’ve found that an adjustment of a couple feet is the most that I ever move my commercial c-stands anyway when used in a lower ceiling studio (10′ max.)
Number three-They’re not the prettiest things in the world. If you’re worried that equipment made from plumbing parts might turn your clients off, you’re probably better off not making these. I have found that you can paint them flat black, wrap the whole thing in insulating pipe wrap or other covering and no body will ever know they’re made of plumbing fittings. Even if you don’t use these as your primary stands ‘out front’, they make great ‘backdrop’ stands and extra stands for holding flags, gobos and reflectors.