Actually if you do it right, you don't even need to turn the water off.
That's it, some RO/DI systems even come with saddle valves. Your pressure should be the same as you normal pressure.
BRS has a video on it.
I read you don't have to shut it off, but that it's best to do so to avoid any leakage.
Sorry mark I do not agree saddle valves are prone to leaks and provide limited water pressure. Go to Home Depot and buy a shark bite and cut it in with a hose bib no soldering easy, safe and full water pressure.
I've used saddle valves for humidifiers and refrigerator ice machines with never a problem.
There's a saddle valve on the line already that hasn't leaked in the many years it's been installed, but I would think the sharkbite fittings share that problem since they use a rubber seal as well?