It's just an option to have the two different chassis. I'm currently running the stock 2.0 chassis and I feel it's just as good as the 2.5mm chassis but if the traction is very high I will switch to the thicker chassis. I also like that I can move the battery around should I feel the need to. That can't be done with the other two chassis. I like the fact that I can tape my batteries in with the BMI chassis.....again personal preference not something that has to be done.