Apple - What is the benefit of purchasing a Mac formatted External Hard Drive?
It's probably no different hardware-wise, just already formatted for the Mac. There's a whole pile of people who still think Macs need special everything, so the companies take advantage of that to fleece them out of an extra £20.
In general, you don't need special Mac-only hardware stuff anymore. Hard drives, RAM, peripherals, etc. are all fairly generally universally compatible; even the stuff that's generally seen as "Mac" (i.e., FireWire and now Thunderbolt) is Windows- and Linux-compatible and will generally work fine.
EDIT: I guess I can think of one good reason to buy a pre-formatted "Mac" drive: if the user is not someone who is comfortable formatting disks. On the other hand, Disk Utility is sufficiently straightforward I've walked my parents through formatting drives a couple of times over the phone, so I wouldn't waste the money.
There is no benefit to purchasing a Macintosh formatted drive because it is trivial to reformat the drive yourself using Disk Utility.
Open Disk Utility.
Select your new disk from the panel on the left. Select the disk, not the partition which appears below it.
Click on the Partition tab on the right.
Important if you plan to use this as a bootable drive, select Options… (under the Partition Layout section) and choose a GUID partition map (assuming you're using Intel based Macs.)
Select the Format which is Mac OS Extended (Journaled) unless you know the specific reason why you're using something else. I would also leave the drive as a single partition unless you have a clear idea about why you're not doing so.
Click on Apply.
None to any user who knows how to format it with Disk Utility. Its just a marketing method to justify a slightly higher cost. Now if you plan to plug it into a Airport Extreme as a external hard drive and don't have a Mac in the house to format it, then it has value.