MacOS Catalina – Spotlight Search Problem with External Hard Drive Mac OS Extended (Journaled)

Unfortunately, Apple introduced a new technology called Core Storage to handle the new full disk encryption. You can read about it in John Siracusa's review of OS X Lion. This new type of volume cannot be read yet by other OS versions, but I'm sure some third party will eventually create some software that will enable reading these volumes on other operating systems.

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.