I worked as a plumber in the 80's, and back then, plumbing was mostly copper or the older galvanized steel. PVC was being used for drainage, and CPVC was available but not legal in some places. PEX did not exist yet, (as far as I know), but was not sold for common household use.
Anyhow, I want to replace the pipes in my own house, which are copper, but were installed poorly and regularly freeze in winter. While considering moving some of that copper pipe, and sticking with copper, I found that copper pipe is much more costly than it used to be. I decided to look into PEX. I have heard the pipe is strong, does not break easily if it does freeze, and fairly easy to install, once the expensive crimping tool is purchased. At the same time, the brass fittings are very expensive, and while the PEX itself appears to hold up well if it freezes, I question how well those brass fittings hold up if they freeze.
I was almost sold on the PEX, despite paying the high price for the fittings and having to by that costly tool, until I noticed the ID of those pipes. A so called 1/2" PEX is really only about 3/8", with the fittings being close to 1/4". That may work fine for a bathroom sink, but I question how slow the shower will run, and know that an outdoor spigot for the garden hose is going to have poor flow. Using 3/4" for everything is more like using 1/2" copper, so I'd almost have to use 1" pipe to feed the outdoor spigot.
I can now see why they use a manifold system when they install PEX, because daisy chaining from fixture to fixture will result in poor flow and pressure.
My house has no basement, so I have to install the pipes inside walls, or on top of the interior walls and hide them with trim, to avoid ripping the whole house apart. Thus, the manifold method is not appropriate because it would require too many pipes to hide.
I've decided to go back to using copper, or maybe use CPVC, which I know is easy to install, but I know it dont hold up well if it freezes.
At the same time, I question how the PEX industry can legally call their pipe 1/2" or 3/4" and so on..... when it's really one size smaller than it's rated. To me, that is false advertising.