Over the last couple of years the Brazzaville to Kinshasa border has become quite a popular option for overlanders. This is mainly due to Angola refusing multi-entry visas so the option of using Cabinda as a transit route gets ruled out.
The Brazzaville / Kinshasa border is notorious. It has to be the most chaotic crossing almost as bad as the Mauritania / Senegal border - if not worse.
As a result two of my friends, travelling in a Defender 110 opted to find an alternative route.
It's worth reading if you are heading through the Congo's: Langebaan Sunset