I don't know about reliability, but I have heard that the trigger pull is obnoxious because in addition to moving the hammer, the Mateba pushes the cylinder against the forcing cone so there there is no bullet jump or flash out the sides.
The gun fires from the bottom cylinder to keep the recoil moving straight back. I shudder to think what would happen if you got a double-charge. Revolvers normally blow out the top. The Mateba should blow out the bottom, and on to the shooters fingers.
As a technical design, it's excellent, and probably worth having for that reason alone.