I guess the intel Macs can use unpowered USB drives to boot from. Maybe it was the PPC models that had to load the USB stuff at boot up, which didn't happen in time to use an external USB drive.
But I would also be wary of an un-powered external drive. I can only assume that it is actually a 'laptop' (lowerer power requirement type) model, incased in a box. Of course, carrying around another cable and cord is just one more thing to leave behind!
Would be great to have a live test to be sure...
Only thing I know is that a good friend who repairs older Macs, including changing hard drives, considers WD as at least second rate compared to Hitachi.
I'm pretty sure my external (AC powered) 500GB drive is a WD. The model and serial number both have "WD..." in them.NOPE! That's the internal in the iMac! The external
is a Hitachi, that's why I bought it!
I've only had it for about a year and no problems at all, Quiet as a mouse (and so is the OWC enclosure).
Finally, I find that most of my 'buy it before the coupon expires' purchases were not as wise as they should have been. YMMV (hopefully!). There's usually a reason things are marked down. Be sure the warranty starts with the purchase and not the manufactured date, BTW! I'd be doing some extensive Goggling tonight for any problems with that model.