"Relining" is bogus. If you have old/galvanized pipes that need to be replaced, that's what needs to be done.

Do it in stages if cost is a factor. I don't think there's a cheap substitute.

If you relined old galvanized steel you would have further reduced the flow through the (in many cases) almost completely blocked line.

I have seen 3/4 inch galvanized line with a lumen barely 1/2 inch wide by 1/8 in high (found by cutting the length of pipe into pieces about 3 inches long).

And the crud ate the metal cutting handsaw blade.

There site states:

(2) Cleaning. The dried pipe is cleaned using an air and abrasive mixture that prepares the inside surface of the pipe for proper bonding of the epoxy. An air and corundum mixture is used to sandblast the inside of the leaky pipe.

That method will literally cause leaks to develop where none were previously there. Then I imagine the sales guy will give you a price to replumb your home traditionally.

We have used a similar method for industrial cooling supply lines or cooling members but only as a temporary solution until a furnace can be shut down and a proper replacement or isolation is done. I would never recommend this for any residential setting for this reason and the others mentioned above in the previous posts.

" An air and corundum mixture is used to sandblast the inside of the leaky pipe. "

It would take days to grind a galvanized steel pipe clear, and eat holes in other places at the same time.

Galvanized steel has a life around 30 years, and once it scales up it is gone.

Keep in mind you do not have to follow the original pipe routing, or even remove the old stuff (any more than required to match up to fixtures you already have and want to keep using).

Cast iron DWV can last almost forever (hundreds of years).
The iron rusts away on the inside slightly, but the carbon left behind becomes coated with waste and corrosion comes to a stop.

Vibration and movement resulting in cracking are the biggest enemies of CI (or very high flow velocity that scrubs the pipe inside).