Does it not have the efficiency of regenerative braking?
Yes, but so does a normal hybrid. On stop-go trips (like town driving) regen braking has a significant impact. On long distance driving it’s minimal. And there the efficiency of the drive train is more important. A regular hybrid drives the wheels directly from the rotational movement of the engine, rather then converting that motion to electricity and then back again to motion.
Edit. The aforementioned Ampera annd BMW i3 REX operated in this manner, but had a 50 mile electric range and could be charged by the grid.
The Mitsubishi Outlander PHEV was similar, but when on cruise the engine had a direct linkage to the weeks via a clutch to improve long range efficiency. Again it was charged from the grid. For those three, you could do all short (up to about 50 miles) journeys on electricity only. You only needed the combination engine for long journeys.
The Nissan needs the petrol engine for everything. All the services costs and wear associated with short (cold) engine trips, no efficiency boost of direct drive for long journeys and not able to charge to be electric only for short range. Seems nuts to me.