Yes, apparently people have found things in YN. I have never found any metal but have seen the blue and red pieces that are supposedly plastic. My Teasel use to decorate his igloo with his YN. T had a loft in his cage where his igloo was and he would carry the YN up to his igloo and line it up end for end all around the inside edge of his igloo. Sometimes he would have 4 rows of neatly placed YN. When I started noticing the same red and blue pieces in his poop that were in the YN, I quit using it. I'm not sure if the YN on it's own would cause impaction but the plastic pieces certainly could.
One of the problems with Carefresh is it ends up in food dishes easier than Yesterdays News. People use Carefresh as bedding and if it gets in the dish, the animal can eat it by mistake. Rarely do people use YN as a bedding because it is really not an ideal bedding as it is hard to walk on and not comfortable to sleep on. Because of this, there isn't as much risk of the hedgehog accidentally eating it so unless they do on purpose it isn't as much of a problem.
One of the problems with Carefresh is it ends up in food dishes easier than Yesterdays News. People use Carefresh as bedding and if it gets in the dish, the animal can eat it by mistake. Rarely do people use YN as a bedding because it is really not an ideal bedding as it is hard to walk on and not comfortable to sleep on. Because of this, there isn't as much risk of the hedgehog accidentally eating it so unless they do on purpose it isn't as much of a problem.