I see a lot of coffee shops and market stalls with iZettle too.

Interestingly Square seems more expensive than iZettle. Square is flat 1.75% in-person 2.5% online while iZettle is sliding 2.75%-1%. The threshold seems to be £6200/month at which point iZettle is going below 1.75%. That's pretty low so I suspect most shops would still chose them.