How to use ESM?

So I’ve been loving the HARM gameplay with France, USA and Israel and was only made aware recently of the ESM on my F18 and M2k but I find it pretty bad to use and awfully slow even more so when compared to prems Su30s that work instantly, am I doing something wrong with NATO ESMs or have they just bad according to the game?

I will add there that I’m not an expert in how they should perform (it do be weird to me the night and day difference between pact and nato so I hope I’m doing smth wrong).