IMO, if buying new, you should always go with the latest version when possible. This [hopefully] ensures the best "future proofing".
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In theory", BT5.2 is backwards compatible to BT4 devices. But there are some newer features/enhancements that don't work with BT4.2 devices.
To me, the most important thing TLS said is,
look for a dongle that supports up to 100m
I agree totally. This also typically means (to me) to ensure the BT adapter is an external device (like a USB dongle) - that is, something that sticks out and away from the case, and not a device that installs totally inside a metal (which provides excellent RF shielding - not good in this scenario) PC case. External RF devices (BT, wifi adapters, RF mice, etc.) ensure the antenna(s) used in that device are on the outside of the PC's metal case.
Internal devices are great for BT devices that will be used in very close proximity to the computer - such as keyboards and mice. But as soon as distance is needed, the external antenna of the dongle is desired.
Speaking of "in theory", I note the specs for BT5.x claim the range is 400 meters! Yeah right. Keep reading and it claims (I'm paraphrasing) the
effective range is 200 meters. Yeah right, again. Then it claims the range is "40 meters indoors". That's more like it, if this is in a very long hallway, and there are no barriers (walls) between the two BT devices.
And while they use different bands and technologies, BT still operates in the very popular, widely used 2.4GHz RF band. This means it is possible other devices could cause interference, which may also affect usable range.
So if you follow the TLS's advice and get an adapter to that supports a range of 100m (328 feet), it should "in theory" easily support the more likely distances (and crowded 2.4GHz RF environments) normally used in homes - which is probably less than 50 feet.
Of course, "in theory" and "real world" don't always jive. So make sure wherever you buy from has a return policy.
