how much for the iMac?
that ext hdd looks good, but i have never heard of them before, and i would worry about who makes the hdd that is on the inside of it.
when i needed an external hdd, i bought regular desktop hdd's (that is all that is inside externals) that i trust. one is a seagate, the one i had in the desert is a Western Digital. and it runs perfectly still.
to me, hard drives are the most important thing in a computer, because if you lose that, all your data is gone. so i tend to spend a little more for what i believe it reliability. IMHO i believe that is getting a reliable desktop drive, and sticking it in a $30-$40 external enclousure.
looking on ebay, you can get a internal 250GB internal HDD with an 8MB cache @ 7200 RPM anywhere between $72 on upwards, and enclosure from $30 or so. i know its more than $70 after rebate for the one you found, but data is important
OT: from the comments for the cavalary external HDD
Cons: 1. Although it is a 250 gig capacity HD, the usable space is about 232 (insignificant gripe; 232 gigs is a huge amount of space).
he is getting 250GB, using 1000KB vs 1024KB. at 1024KB it would be around 230 some. . . just a gripe i have when people complain about it.