If you are normally based in the UK (or even more so if the US) and are doing it to save money I wouldn't bother. You might save a small amount but with the hassle of getting it back here (assuming you don't even pay the import duty), the hassle of returns if it has a problem, etc. I can't see that it is worth it.
If you really want to do it then double check precisely how much the same spec would cost you at home and then take that info with you to the Funan Mall.