You can adjust the pressure of the gas spring on each arm individually to the weight of the monitor.So: Yes, you can hang monitors of different weights.

I have the holder and have 3 different monitors. I once had a 30" monitor on one arm, but it was rather too heavy.
So to answer your question: It doesn't matter if the monitors are the same weight.

The arms don't need a counterweight or anything. From that point of view, I would say it should work.