Verdict
Identical mechanics, electronics, AMS compatibility. The P1S adds the official enclosure + active filtration. That changes the printable material list dramatically.
Buy the P1P if: mostly PLA, occasional PETG. The DIY route — print your own enclosure later if you ever need ABS, save $100 today.
Buy the P1S if: you'll print ABS / ASA / polycarbonate within 6 months of buying. Day-1 enclosed is cleaner than retrofitting later, and the active filter helps with the styrene smell.