Cheaper, but without power supply.
And nope, it doesn't use stm32, but STC, won't work.
The main differences between v2 and v3 is the screen type, spi vs i2c, and few circuitry differences, sometimes better and others worse, can't tell, there're a lot of variants.
There's no such ARM chips. ARM sells the cpu design, doesn't make chips.
Chips containing ARM technology usually also have ARM labeled, stm32 do.