I do not believe the lens has been modified on passenger, it was a complete redesign for the pro though, they did not just add a field flattener, they incorporated it in to a new build (per Agnes)
The Passenger model will be gone in a few days. They changed not only the chip but the lens as well, as now the description for the lens is the same as the Pro model. I could be wrong, we'll see.
The Vespera pro model will be better suited for smaller DSO objects, the Sun and Moon, as it will have a longer focal length and significantly better resolution due to the smaller pixels. Conversely, the Vespera Passengers will take faster photographs of nebulae with a better Signal to Noise ratio.