If the parcel is stopped and checked, you'll get a notice from customs advising you that €XX is due. Exactly
how they calculate the amount due is a bit of a mystery, I'd be guessing maybe €25/€30 or so? Effectively enough to cancel most of any saving.
Whereas if you order from inside the EU, the tax and duty is already paid and there's no further liability. Also, for a product like this which
might give trouble, I'd say that Amazon's excellent customer support and returns policy make it worthwhile to pay a little more than the likes of Dealextreme or Chinese eBay sellers.
There's a big thread over on Boards.ie at the moment about an [broken link removed], if you have the patience/interest for it? But a lot of the posters seem to be experiencing long delays/poor communications from sellers.
The tablets usually have 2GB, 4GB or 8GB internal memory, but they also take
microSD memory cards up to 32GB capacity (20/30/40 movies, depending). Most of them have a mini USB rather than a normal USB slot. You'd just need a cheap
adapter. For the kind of use you envisage, I wouldn't worry overly about getting the highest spec/best features available for the price. Your kids won't notice the difference, or complain that the touchscreen is resisitive rather than multi-touch capacitative.