I have been using it for about a week and can say that it makes things look so much better. I really hope this doesn't get banned in the future (can't see it happening, like FXAA injector) as it makes the game so much nicer to play.
People may and do think that this is an unfair advantage but from what I can tell, having tested Colour Tweaker and going back to stock, that there is no benefit in seeing people. If anything on some sections ie inside the metro, the Colour Tweaker actually makes it harder to see people in the dark bits.
You may need to change some in game brightness depending on the monitor you have. But In my opinion EVERYONE should use it and enjoy actual colours in the game rather than dull blue.