I think the IM code is the same as in the UK. My (UK Maplin bought) 1004's full description is IDE1004IM.
It should work all right, but you may have problems with
DVD region codes, if you want to playback non-US DVDs but the Dangerous Brothers firmwares (search this forum) are supposed to put that right.
Warranty repairs, you might have to take it back to frys or send it to the USA BTC repair depot with all the uncertainty and delay and cost of transatlantic shipping. Not sure about that one.
HM Customs can charge duty on goods worth more than Â£18 from outside the EU. I think, other than the tobacco and alcohol allowances, you can bring in Â£145 worth of "gifts and souvenirs". It might be wise to check this. You can get done for smuggling if you do not declare things. People get laptops confiscated and heavy fines.
With the Â£ - $ exchange rate as it is at the moment (around 1.80) you may still be saving some money In the UK, Maplin are selling this drive "on promotion" at Â£79.99 inc VAT with free delivery.
Moneywise, the bottom line is you would be saving around Â£35 if you are not charged any import duty.