Not really sure about AData, but with RM175, can get WD Blue 1TB from a forumer already....

oh.... thought you were mentioning about 3.5" internal hdd 

then i am not so sure, never bought any AData ext hdd before, only got Buffalo, Toshiba and WD.... 

I met a clerk (girl lai de) very lihai at assemble those CPU, scary see-ing her tear off the clips.. haha. *ahem* back to main topic...

You will need to ask about the warranty and stuff, whether you gets 3-year or just 1-year, possible some won't entertain warranty or some shop has very bad RMA experience, just sell cheap only.
Other than warranty, yes, it's a darn good deal for 1TB 2.5" external HDD.

You're buying from advertisement at Groupon?
It's understandable that Groupon sometimes much cheaper but I wonder about the service.
If the retailer is reputable one and they have good history of providing good RMA service then I can say, go ahead with the purchase.
I myself still buying from local retailer due to ease for RMA service, but recently has bad experience with PC Image so I'm avoiding that for the moment.