So I've just been using basic earbuds my whole life, never felt like spending big bucks on good headphones. Recently though, I've been really interested in what I've been hearing about IEMs. Youtubers and forum users have been name dropping a few of them, such as Moondrop Chu/Chu II, Salnotes Zero, etc. So I looked them up, and was shocked to find how cheap they are. They're like $20, in the same price range as the crappy earbuds I buy anyways! These kind of headphones seem like a whole world I know nothing about, with pros and cons I don't fully understand, so what would be the best recommendation for a first set?

I'm looking into the ATH-M40X, which seems to be the best below 100€, but i would like to know other tilders opinion :)

EDIT: preference to over ear and portable (portable is not a key feature that i'm looking, but it would be nice to be easy to carry around)