I've heard conflicting things about that 1.5TB from Dell, some claim it is built with lesser standard parts. I note it only has a one year warranty and it's specs give it a maximum room temperature of 95 degrees F. Also, if you have an older computer (like mine) it hangs up with trying to boot up with a large USB hard drive (in my case a 1TB Maxtor). Simple solution once you know the problem, just disconnect the HD before booting but it's annoying.
Personally I think externals are fine for music storage-I've used them for years now and they run 24/7/365 in an unairconditioned room. But backup it always essential, because hard drives DO fail.
At this stage I'd wait a bit for the Black Fridays ads to see what deals are up. It's pretty common now to get a name brand 1 TB USB only external for $90-110.