doesn't work in my o2 locked phone
I went to GT Mobile from GiffGaff for that very reason... I would say GT Mobile is better, but it's very much dependant what time of day I run speedtests. Right now I have 11 meg which is great, but if I check later on at work I'd be lucky to get 1 meg. A colleague who sits near me is on o2 and has no speed issues, understandably.
If you go by the reviews than tesco and gt mobile data speed are much better than giffgaff(they all use o2 network).
Can anyone confirm that the 4G will be any worse than giffgaff? My giffgaff 4G is lovely, (I live in central London). Also you tried to tether? I know it's against their policy but wondering what happens.
I moved from Giffgaff to GT Mobile (which is actually owned by Lycamobile). Can confirm it runs on the o2 network. It's great value for money, although when it comes to data speeds expect to get around half a meg download speed at busy periods of the day. In other words, you're not going to have a good time watching Youtube videos on your lunch break :)