> I'm not familiar with how Orange, the biggest operator, functions. But I understand they have a general tendency to be a PITA so YMMV with them.

I can only attest how they work here in Spain: They're not the best in terms of the 'openness' of their hardware: (in Spanish, feel free to us a translator) https://bandaancha.eu/articulos/router-pone-orange-jazztel-s...