Air/water separator as an oil catch can?

I’m curious to know what kind of experiences you people have had on using an air compressor air/water separator as a primitive oil catch can. I’m soon probably going to spend 10€ or so on a filter to get my own impressions on the subject regardless, just to prove the point either way.
Many people online are claiming that they do in fact work(at least to an extent). But then why would this cheap alternative be overlooked? People are buying +100$ kits and not complaining about the pricing, which makes me awfully suspicious.

All feedback is welcome, thanks in advance.