With the dollar being so weak it is a good time to import from the US. However, you still need to allow for 40% extra cost due to freight, duty, handling fee and VAT. Then you have the problem of items such as GPS having US base maps, radios not being CE marked, warranty follow up etc. Even so, it can be good deal depending on the product and the deal you are getting.
Check the complete price including buying a chart catridge - many places were doing deals inc a Cmap cart in the price, might make quite a difference to the relative pricing of the US plotter Seamark Nunn (where I got my Navman from last year but am only a customer) are still offering a chart cart for £50 with a plotter, worth factoring into the equation. I'll bet other suppliers are doing a similar deal as the deal is probably funded by Cmap to boost the NT+ sales in the runup to MAX being the prime product.
The price is $599 BUT there is an extra mail in rebate discount of $175 making the cost just $424 or about £230. This price is the deal through main Navman Dealers in the USA and the Navman mail in rebate is for US buyers, so you will need friends or family to help. If you ship it you will have duty/carriage and VAT to add unless your US 'friends' mail it to you marked 'gift' for your birthday. I have just fitted my £380 Navman 5600 (+/-£700 in the UK) which our grandkids bought us for our joint birthdays (true!) during our visit there last month.
Don't believe the rubbish and scare mongering in UK mags about USA background maps, they come with a world map but in any event you will need to buy your own cartridges from C-Map. Do your own research about warranty validity, the implications from Navman are that it is worldwide but Navimo/Plastimo UK may not agree, I'm trying to get Navman to state their policy but they haven't replied to my e-mail yet.