That's what I have been using for about 2 months now with no confirmed issues**. Got a 1TB My Book drive for $100 at Staples (excellent sale!) just as the 5.24 SW version hit to enable the higher capacity, which is still the limit for one drive connected at a time. I too am concerned about the long-term life of this drive which was not designed for 24/7/365 use, so I'm not recording anything on it that is "irreplaceable" to me. (Using my 622 for that instead, like sporting events.) As soon as I see that price again I will buy another "just in case". (I think one of Murphy's Law's corrolaries says something like "if you have a spare you'll never need it...!") Mine is about 40% full at this time, mostly HD movies and regular programming, but I have a lot of junk to watch once and clear-off...
**I do have some issues that I only noticed after attaching the HDD, but I have not confirmed they are caused by that drive. On some talking head / news shows the scroll at the bottom seems to "stutter" a bit, and about 1x per day I see where the whole program locks-up for a couple of seconds, then the screen goes blank for a few more seconds, then the whole thing restores itself with no further issues and no action on my part. These things happen whether I'm watching recorded or live programs (???)