Confused about headphone impedance

I have a guitar multi effects that has a headphone out with 47Ω

I want a budget somewhat neutral headphone to use with it and I am getting confused with the answers I found so far.

The AKG K240 mk2 (55Ω) seems to be a popular choice with people who own another multi effects (HX Stomp) with a different impedance (I think it's 12Ω).

This headphone is within my budget, but it seems too close to the 47 output of my multifx.

Will I have a problem with this?

I read somewhere that the headphone impedance should be much bigger than the output impedance, but another text I read somewhere explained that they should match closely.

I'm really confused about this.