As Alex said, changing the shower drain to PEX (or just replacing the hose at all) is a PIA to access and replace. If you don't have to do it, I wouldn't. Make sure you have a strainer on in the head to clean out debris. I did change all of my hot water to PEX because the existing hose and hose clamps were not ideal and prone to possible leakage when heated. I also installed a temperature regulator/mixing valve to control hot water temp. I kept the regular nylon reenforced hoses on the cool water lines. Unfortunately I have a lot of stuff going on under the sink with my Echo Charger and negative busbar living under there behind the door as well. Very tight!