Hi name is Dave and yes, it's silicone. He also did extensive extreme pumping -- the pumping damaged his blood vessels and that's why he couldn't get hard; it had nothing to do with his silicone.
It is true that he and Mark had their silicone removed, but neither had negative health effects from it. Dave had his removed because he got a massive injection from a 3rd degree sunburn to his cock. Instead of going to the doctor, he let the skin wounds get infected and then tried to treat it himself. He ended up with gangrene in his cock. They had to remove a decent amount of tissue, and to get all the infection out had to get ride of the silicone too. But, the silicone was not a problem or the cause of his misfortunes.
As for Mark, he simply decided after having his for 7 years that he wanted to be able to fit in more normally again. It was a personal decision dealing with his life and family. Ask him, there was nothing wrong with his silicone.
It's a different look, and everybody gets different results. Some people love it, and some people hate it. Personally I love it, but to each his own.