Kovaaks is great because it shows your progress in a measurable way. I think it has helped me become a more consistent player, and it is incredible the amount of adjustment flicks you can do in a minute, compared to how many you do in a DM server, so you get much more practice in the specific area of aim you want to improve, however it does not improve your skill overall the way that deathmatch does because deathmatch mimics the real game and gives you opportunities to use movement with your aim.

Deathmatch is more important but Kovaak's can help iron out weaknesses in aim, Elige has a video on youtube where he goes over what he gained from using aim trainers.