They need Active Cooling and protection from Vibrational Damage. I've had to pay places like On Track thousands of $ in the past to recover Data off dead HDD that where used this way and on just about every occasion they where dead 2.5 Inch Drives.
Will the company accept the need to spend 56K to recover data quickly that is what I paid for a Priority Recovery a couple of years ago when the place got robbed and the only current Backup Drive was dropped and rendered unusable. They had an Audit at the Tax Office that week and just had to get the data recovered. Event hen I walked into the Tax Office an hour Late with the Data but at least it was there.
I'm not a great lover of external USB HDD even though I use one myself but I only have it in when it's in use and even then it's in an Actively Cooled Enclosure a MX1 from Antec. Not cheap but lots of capacity as I use 1 TB Drives. At least the drives never overheat though they are still subject to vibrational damage if knocked about.
Personally I still use a mix of Both Tape and External ESATA Drives the ESATA Drives are much faster but not as reliable as the tape and even with the Tape I always have the same Make Model Drive as a spare. When I am reduced to 1 Spare Tape Drive I go to a different Tape Backup Solution. While I've only needed the tape a few times in the entire working life on every occasion it's been a [b]Life Saver[/b] and it's much cheaper than having to have a HDD recovered.
I find the ESATA as Fast but not overly reliable Backup but maybe that's just me I prefer NAS or that type of thing with Hot Swappable Drives if I'm using a HDD Solution for a company and even then I always chose Cloning Raid Arrays not Stripping.
Not the cheapest but certainly the most reliable and with the costs involved in recovering HDD it's much cheaper when it's really needed. ;)
[i]edited to add[/i] I use those cheap USB Drives as over-sized Thumb Drives. They are cheap easy to use and doesn't matter if they cark it. I just personally wouldn't want to trust them with Important Data that couldn't be got elsewhere though.
Col