The Marseilles style belt is the safest of all freediving belts.
The flexible rubber belt adjusts to the compression of the divers suit at depth, ensuring that the buckle does not slip around the body. Because of the small diameter holes and the pin flicking 90 degree to the belt on release, the chance of the buckle re-engaging is minimal. The roller buckle, while always releasing on demand, will not open when dragged past rocks or the gunnel of a boat.
Check out the below video on how to set up your belt.