The difference is:
1. Full balance of the inertia forces and moments of the single-cylinder two-piston PatOP basic module.
2. Zero total force on the crankshaft main bearings from both: the combustion loads and the inertia loads.
3. Additional time for the injection and the combustion of the fuel, that is higher revs, that is higher power density. At the lower revs this extra time improves the fuel efficiency and the clean exhaust.
4. More compact engine: the crown of the lower piston almost reaches the crankshaft.
5. Lubrication quality and mechanical friction equal to the "full" crosshead version of the Junkers-Doxford. The two-stroke PatOP engine has "four stroke like" lubrication.
6. For a given asymmetrical scavenging scheme it needs smaller crankpin offset (less vibration and friction).
7. Built-in volumetric scavenging pump of lower cost and friction.