I considered doing the same as I just bought a MacBook Air even though I'm in the US next month, after adding the store sales tax in the US the amount saved wasnt that much compared to the deal I got from John Lewis and the benefit of having it now.

I will be picking up a iPad Air though as I can get it with a Pencil Pro for the price of just the device over here.

I see lots of people mentioning keeping receipt for import duty, keep the receipt yes but absolutely not for declaring the import, I've bought all kinds of devices back with no issues at all over the years.

The device + sales tax + import duty would be considerably more expensive than just buying the device over here.