Honestly, M31s is enough for a daily user, go for the M51 ONLY if you want super long lasting battery, like 2 days of battery life. Otherwise it is just a bigger M31s, and yes, if you want to play a lot of super high games, then M51 is for you, and if you want super maltitasking experience with normal to high gaming, then M31s is for you.
Coming to A series, you will get bettwr software features, Knox softwares, customization softwares etc. but will compromise on battery.
