Sadly playing back BDs on a desktop is not as easy as DVDs, but it is doable. There is a lot of cryptographic trickery going on and some mechanisms to make it not consumer friendly (e.g. inserting newer BDs can revoke certificates of the (legal) player you use, making all you're BDs unplayable until you update the player).
A lot of people use software to handle the decryption and rip the contents to disk so they can play it any time with any video player that supports the content. This does require quite a bit of storage and sort of negates the benefits of physical media IMHO. Also, if I'm not mistaken, ripping, even for private use, is illegal in the UK (?)
Another option is to acquire the specific key that belongs to a BD. Quite a few keys can be found on the internet, but there are methods for extracting these keys yourself. Again, I'm not sure on the legality in the UK, but in theory it's just a big number that is also present on your BD (although encrypted) and is not really circumventing DRM as it simply speeds up the process by skipping a few steps (IANAL).
Personally, I use the second option as I simply want to pop in a disk and play it on my Raspberry Pi, which is connected to my TV. There is just something really nice about switching disks while binge watching a show.
If you do plan on buying a BD drive, there are a couple of things to watch out for:
- If you plan on ripping, try to find a drive that does not have a rip lock
- If you plan on playing back using keys, try to find a drive that does not support bus encryption (as that will require a valid host certificate, which are not as easy to get by)
- When buying an external drive, make sure the power supply is sufficient (especially when ripping), preferably not powered via USB.
- For normal playback USB2 suffices as it can easily handle the bitrate of a BD.