Let's say you have two memory sticks that are the same size and DDR type but from different companies and stuff, if the PC works, do I have to worry about anything?
The chance of having a working mix-match RAM kits is about 60-67% according to my experience.
You will still need your luck
If speed is different, it should work following the slowest kit.
If it works, it works. If it does not work, it does simply not work.
Nothing to worry about.