I would not characterize TrueNAS and ZFS as simple.
Yes the GUI attempts to make setup and normal operations straight forward. The GUI covers most things and some users may go their entire life with TrueNAS experiencing no serious problems. Plus, as software development continues, the GUI and other aspects should improve.
However, I recommend every new TrueNAS user assume that during their TrueNAS’ life, they will have to both drop to *nix command line and perform ZFS or other storage related commands. Poking around now to see the command’s output, (when not familiar with them), can reduce future stress.
Your familiarity with *nix helps a lot compared to some other users.