Hatch Yaris here in Canada, doesn't have side curtain airbag, even as an option. Sedan Yaris has it in option, but only with all possible options together. Still trying to understand Toyota's mentality....
Yaris has indeed a lack a stability in emergency handling, the car is very light - especially the rear half, and also the rear suspension is too soft. However, one nigh on the highway I almost crashed into a deer. As I saw it at the very last moment in the front of the car (was running across the highway) I had to violently turn the steering. Well, the car managed to stay on the road without rear sliding! Only the tires were non factory (changed for Michelin).