I have an RO system that feeds a separate spigot at my kitchen sink and my refrigerator. Installing it is really simple because it just uses sharkbite connectors that just push to connect. Later on, I added a water heater so that I could have on demand hot water at the spigot which is also nice.

I have a separate filter that takes care of my whole house but that is just a carbon filter meant to scrub out the chlorine (I'm on city water) . Installation for that took a lot more effort and planning.