general power fc questions

[Fenvy]

I see that most people that sells apexi power FC mentions its date, serial number and model number.

So the newer ones are better? what's wrong with the older ones? can I just get the older ones as it being cheaper?

is the black top power fc interchangable with notch top? how about red top?

do I really need the commander?

lastly, power fc can dictate my rev limit right? if I want to set rev limit 7200rpm for all 5 gears, this can be done?