Did your grandpa teach you how to solder? I get it, I still do the old way for the visible spots under my sink, just for that same feeling. The hidden stuff gets the quick fittings though.
Why would you use quick fittings at all? I solder every joint, even the hidden ones. That extra minute with a torch means I never worry about leaks later. Those push-fit things feel like a shortcut that could bite you. If a method works, why change it halfway through a job?