Its a better deal for those in the UK because the warranty is valid there. If customs is on the ball, you will pay import duty to the USA, its small, a few percent.
The big issue is the cost and time involved to return it or get it repaired, and it has developed a reputation for problems with internal lens elements coming loose, and decentering issues.
I'd pay more and buy one locally where I could exchange it. Its probably a better alternative than the original Canon 24-70mmL, but will likely have lower resale value.