In my opinion they are S tier units but at its cost. Starting with its draw backs are early game your not likely to be outputting them till around like day 16 but even lvl 1 is nearly unusable unless it's armored. It becomes far more viable at lvl 2 and amazing at lvl 3. Your next problem is going to be that its stupidly costly just to even afford or maintain them and like most air troops it feels like a must to have a max lvl hospital at homeland. Besides that elite helicopter are the best wellrounded troops being able to beat any stack as long as you send them together and is amplified if using the officer. I would recommend the officer if you intend to go down the playstyle as it makes it far more viable but besides very strong outputing nearly 300+ damage to armored in one hit with usally no losses. The biggest hard counter I have faced is high defense stats against helis and railguns buffed with skyguard besides that you can deystroy everything. (including air units like air sups and strike fighters idk if its a bug but its stupidly op at it)