I always advise him a good mileage vary depends on traffic condition & route one use. beside this, this is a DOHC engine (which means everything also double)

Vios 2018
Before 1st servicing, mileage is 15+- km/l
But after 1st servicing till now.. is always at 10+ to 11+- km/l
Worst than before 1st servicing and also his previous Vios
Brochure (see website) stated 17.2km/l (base on ??)
This model is 3kg lighter than GK5
my guess is his driving style is 50%/50% ba.
GK5 2018
Best score is 21.7 km/l (70% highway/30% city)
Worst score is 12km/l to 13.4 km/l (100% city)
brochure stated 17.85km/l (base on ??)