That system is one small electric motor bonded directly to a gas engine, using a single shaft which requires both components to always rotate at the same RPM. That lack of independent operation limits what's possible. The system doesn't have a second motor either, which further limits abilities... like recharging the battery-pack even when motor power for the wheels is needed. In other words, that "electric only" operation is brief and only occurs on spans of road that require little power to sustain the current speed. That makes crawling through stop & slow traffic is pretty unrealistic, unlike Prius which thrives in those conditions.
