I ship a LOT of product overseas. I use US Mail for all of it and it's done me pretty well. I generally only ship smaller packages, but for larger ones I haven't had any issues (I think I've had one or two packages lost out of thousands, as I used to sell on eBay as well as a private party).

A few pointers:

I've found that to some countries Global Priority Mail is just as slow or fast as regular Airmail, while Surface can easily take up to 3 months to get to the designated country. Also, keep in mind customs when shipping overseas. Your customers might have a fit when they realize they have to pay tax on things they import.