alt Hacker NewsLighter weight does improve range a bit in stop and go city driving, but not really on longer trips. Once the weight of the car is up to speed, most of the energy is spent fighting aerodynamic drag. Lower weight would probably reduce rolling resistance and has other benefits to vehicle handling and costs.
I doubt a sub-1 tonne car is going to be pleasant to drive at highway speeds (thinking about the noise insulation here) and especially if there's even a little bit of wind. This is clearly designed for localized city driving. I suspect that it's also more (though not totally) pedestrian friendly in that the kinetic energy stored will be far less given any kind of impact.
I personally love that it is running counter to the trend of car masses and sizes increasing across the world [0]. There's a reason why there's a small, very fun and niche community of Kei car enthusiasts - the case against pavement princesses and absurdist masculine performativity is a strong one.
[0] https://hannahritchie.substack.com/p/global-car-economy