I have fluke multimeters that can measure that low
If a Mosfet fails at .03 ohms then you would have magic smoke rolling out of your mod and possible loud pop.
If a Mosfet is slower than the other one, then you are gonna get a one mosfet that will get warmer than another, but we are talking in ms, it wont make that much difference.
If one battery fails then you will not get that high of wattage, because of voltage drop, and you will strain the other battery (downside to any dual battery unreg box) VTC5s are rated for 150A @ >3 Sec (Dangerous Load, but i do not know anyone who could vape @450W)
And when you pull 450w of current the batteries would stay at 4.2V i measured at 3.7 to account for voltage drop under load
Basically this box is capable of delivering high power. It is over built I don't plan on using it at is limits