in the instance with my G5 it was in stock in the shop I first clapped eyes on it and knew it was a gun I wanted, but with effectively saving £250 on that order (and if you include the other 4 mags I ordered seperately £350 total I saved) I have effectively got the gun for free.
In an ideal world I would buy from the UK for all my toys, but with that sort of saving, limited stock in the UK and in most cases still having to order online and wait for items to be delivered (normally when I am out so I still have to go to the Parcel Force office to collect) buying from outside the UK is a no brainer on SOME purchases. With the RM4 as has been pointed out I didn't save that much but I still got the gun before I was able to find a UK seller with it in stock.
I have a friend who is able to sort me items from the US (not airsoft guns anymore) which means I don't normally have to pay any shipping or handling charges etc from bits I order from America. I am getting my HPA set up this way and with the Dollar/Pound the way it is the delay is worth the saving.
I don't want our UK based shops to go out of business, they are a valuable asset but I am not going to throw money at them without seeing how much I can save from other companies first.
I actually bought my TM MP7 and TM G18c from the UK and in the case of the GLOCK it has proved a wise choice as a couple of mags started leaking which I dropped in to them and they fixed while I waited FoC, there are def advantages to buying in the UK and to buying abroad, people just need to be aware of the up and downsides to both ie: UK suppliers are generally more expensive, have less stock and you don't always get free postage, buying from Taiwan for example means less warranty support (although Samoon are amazing), slightly longer delivery times, shipping can be expensive and the Parcel Farce fee is a rip off, UK Customs are a PITA but they don't rip you off and the VAT/Import Duty is not excessive.
Currently if I was buying another RM4 and I could get it delivered to my door for just £30 more than ehobby-asia would charge me I'd possibly buy in the UK, it does massively annoy me that an item can be shipped in from the other side of the world as a one off order, eg single gun, for less than a UK shop will sell it for over the counter. Even the UK online only shops which have far less overheads still cost more.