I bought a dynamite SS screw kit a few years ago and changed out the screws in my ruckus and circuit. I agree that the SS metal is softer and you have to be careful when using an Electric screwdriver, or to not over tighten with a hex driver.SS is okay but the metal is actually kind of soft-- it's why cutlery with SS blades need constant sharpening. I prefer black oxide fasteners-- harder material means you're less likely to warp or round out the hex fittings. The oxide coating makes the hardware less susceptible to rust but not rust-proof like SS.
By and large though, SS fastener kits with hex fittings will be a huge improvement over typical stock fasteners in most ECX cars.