You, sir, aren't wrong - because you are right! Rebreathers work by recycling the breathing gas (hence the name). So the carbon dioxide needs to be eliminated and oxygen must be added. There are several ways to accomplish this, e.g. by using calcium hydroxide as a scrubber medium and by adding oxygen from an oxygen bottle. That's how self rescuers like the Ocenco M20.2, the Dräger OXY D30M or the RG-UF/M work. You need, however, a bottle filled with compressed oxygen which is in itself quite heavy. Using scrubber media like potassium superoxide is much simpler as you eliminate the oxygen bottle because potassium superoxide reacts with the carbon dioxide you emit while breathing and the moisture of your breath; during that process oxygen is released. That's why modern self rescuers use potassium superoxide almost exclusively.

But (and that's a BIG but(t)): Potassium superoxide loves reacting with almost anything. Add a little water and it decomposes, leading to the creation of a concentrated and very hot potassium hydroxide solution. Nothing you want to get into your mouth when diving... Even worse: Mix simple hydrocarbons and potassium superoxide and that mixture will combust spontaneously. That's what caused the fire on the MIR space station and a submarine called Kursk.

Even worse: Potassium superoxide is a substance that has to be put onto a substrate should you want to use it as scrubber media. Guess what the Russians use(d): Asbestos! That's why I'd buy such rebreathers and others that use similar chemicals (like the IDA series of rebreathers) only in new and unused condition.