on 07-06-2019 20:54
It's usually because other retailers don't offer Refresh, flexible tariffs and some discount schemes.
However, everyone should go for the deal which suits them best.
If it is cheaper and is what you want, then you should go for it
on 07-06-2019 21:21
OnePlus 6 (O2 & Sfr), Z3 Tablet (Three UK), iPhone 8+ (EE)
on 08-06-2019 01:14
If you can get a tariff you are happy with and aren't bothered about Refresh then go for the best deal. Bear in mind though that you need to check if it's a 2 or 3 year contract and don't forget with O2 once the device is paid for you pay only for airtime.