I've used them 4 times and never had a problem with taxes.
You get 5% extra off if you order 3 or more items. Also, you get an additional loyalty discount, 1% after your first order, 2% after second ... 5% after 5, 7.5% after 10 and 10% after 20.
Prices are a bit cheaper than Irish duty free prices (which I've found are cheaper than most duty frees). Each item comes gift wrapped in silver paper and the package itself has a blue ribbon around it. Usually arrives around 4 or 5 working days after ordering.
Highly recommended.