I have recently bought a Rock Pi 4 mini-PC from Radxa in Shenzhen (literally, I went out to their office and bought it from the development team).
The Rock Pi 4 is similar to the Raspberry Pi but it has more memory (I bought the 4G model) and a faster processor.
Here is the board with the small heat sink added:
Radxa now have a larger heat sink available.
Radxa also sell a case for the Rock Pi 4; it may be a small board but it takes lots of plugs:
I bought the Rock Pi 4 as a mini-PC, as a smaller (and cheaper) PC so I will discuss it in that context. The Rock Pi can also be used for education or hobbyist purposes, like the Raspberry Pi.
I bought my Rock Pi 4 just after the release, so some issues may have been fixed by Radxa already. I am running the 32 bit Debian kernel, and results may be different with the 64-bit Ubuntu kernel that Radxa have now released.
The Rock Pi 4 started immediately when I had unpacked and installed everything. It brought up a desktop.
I was able to install a development toolkit for Go (golang) and build my applications.
The Rock Pi 4 runs noticeably faster than the Raspberry Pi 3B.
Not so good
The latest version of Chromium does not work on the Rock Pi 4. This is a general problem on some ARM systems (it is a Chromium issue). The work around is to downgrade to an earlier version. To downgrade, check available versions using:
sudo apt-cache policy chromium and then
sudo apt-get install chromium=*version*.
You want to change the password on the default account.
The Rock Pi 4 is a good buy if you want a box that is similar to the Raspberry Pi, but more powerful, and you have some skills in Linux system configuration.