This product sounds stupid. I dont believe a MAGNET would help with PE, but I've seen MANY posts talking about something similar called a "Ring Of Power". It's basically two different short metal rods (I believe zinc and copper were considered practicle) that are connected at each end using silicon tubes, forming a "ring". You then put it around your dick, at the base. It creates a current through your penis exactly like a battery. If you make it, remember to polish/get rid of the top layer of metal every few days because the chemical reaction will only happen with the pure metal. Once the metal has been reduced or oxidised (ie the reaction takes place), that metal can no longer react.
The current which is near your testicles stimulates the production of semen and testosterone. I've heard that wearing one of these is a good way for men to get in shape as well. I've never made one, but I know that it works because I tried making it with a AA battery and two copper nails (which makes a U shape) instead. I didn't feel anything for a few minutes, but I got a huge hard on shortly after. I don't recommend using batteries, it seems to have too high a voltage (1.5 V vs 0.7 V that I've read people were getting out of their ROPs). You DON'T want to fry your sperms.
I haven't bothered making one because I'm 20 and I seem to have enough testosterone.
This will not make your penis larger, but it will increase the testosterone, which increases the release and effects of erythropoietin, increasing your RBC count. If you are perfoming PE (or are weight lifting) it should theoretically reduce the time needed and increase the efficiency of your body's recovery. It may have other benefits of which I'm not aware (I've only done my first Physiology course lol).
DON'T SPEND MONEY ON COMPANIES THAT HAVE PRE-MADE ROPS's. If you look hard enough on the internet, you'll can find a detailed article on how to build one.