I am not telling him to use that, he asked if the car can run on that, and it can. if you want the best for you car and keep it in top condition you'll use the manufacture recommend specs.

Yes, the car will perform better, and burn cleaner with 91 octane. But he can use 89 with it, with no problems. But I don't see the point, he'll be saving about $3 per tank anyway which does not make sense, believe it or not if you use 89 you'll get less mileage than using 91, so it work itself out.