It's okay to mix between Brands. Eg SHell,Mobil,SPC etc
But try not to mix between different RONs. Opt for one and then
stick to that particular RON.eg, 95 or 98.
I'm driving a 12yr old 1.0l car.Its giving me at least 16-20
km/litre. On an average month,I spend abt $160 on petrol.