We normally use cable ties (you can buy very colourful ones in Home Depot in the US - pink, yellow, orange, turquoise) and we have still had our suitcases opened, and the ties have never been replaced, so I do not think that this is a guarantee that your suitcases will be left alone - they have the right to open your suitcase so you just have to accept that.

We use a TSA lock AND cable ties now, but expect at some stage to have the suitcases opened on the way. Incidentally, we flew via Charlotte 2 weeks ago and returned 2 days ago and on neither flight were the suitcases opened.

The best advice is not to pack anything valuable in your suitcase and I think this is true wherever you fly to - be it the USA or Europe or the Far East. It makes sense to carry precious items in hand luggage and then you can be sure that they won't disappear. Doubtless there are many cases of theft at our British airports, too - and if your suitcase has been opened in the USA, on the way back there would be ample opportunity for the thefts to take place on arrival in the UK if your suitcase is unlocked.