You have nothing to worry about.
I bought an IWC at Mappin Webb T5 at 25% saving compared to High Street prices. So for your Omega you'll probably save 500GBP on a good day. The US price will be similar considering the weak dollar, unless you know a good dealer and can score bigger discounts.
Don't forget that the watch comes in a bulky box, with certs etc. inside. You want to keep the box, in case you decide to sell one day. I had my box in the carry on when returning.

Good luck.