The selection at dutymall.com offers is good and the quality of the products is as you would find in any "regular" store. It's pretty simple to order and there are plenty of payment options.
If this site has one advantage it's the duty free cigarettes prices it offers that can really save a lot of money. For casual smokers like me it saves a pretty penny but I guess that for smokers who smoke more than me it can save a lot more, so it's definitely recommended.