We run on the O2 network, so 4G coverage is standard.

Is giffgaff as good as O2?

Giffgaff's coverage relies on O2's, which means it's currently at around 99% 4G population coverage indoors. That puts it behind Three and EE and in line with Vodafone. Giffgaff also has strong 3G and 2G coverage, so you should be able to get mobile data of some kind almost everywhere.

Are giffgaff and O2 the same?

A provider that is held together by its community, but is not a network holder itself. It's what's called a mobile virtual network operator, or MVNO. It runs on the O2 network, which means that, as a giffgaff customer, you'll benefit from the coverage and 4G/5G speeds that O2 provides nationwide.