Yea they are good. I use izettle and can highly recommend it.
I have in the past use the traditional chip and pin mobile terminal and that's a bit hit and miss with Mobil signal, but izettle uses my own phone signal and very rarely have problems with it.
The one I got connects with a wire into the headphone socket of my iPhone, but they do have Bluetooth connectivity ones, and also the ability to use contactless and also apple pay. With no monthly fees, nor rental and only pay for the actual transactions you put through, like you say, it's a no brainier.