The reason they are cheaper is the quality is not as good. These are factory seconds. In Orlando you can find factory outlet malls that sell everything from shoes to TVs. They are real but they have minor defects in the quality.
The phones should work in the UK but you may need to pay to have them unlocked, about ��10. The real issue is what do you do if it breaks or doesn t work when you have been back in the UK for a few weeks. Most international brands do not warranty goods outside the country of sale. The store is unlikely to respond to calls from so far away. How will you get redress?