Which keeper or eco-tampon is best to choose? Caoutchouc or silicone?

Recently I read that the eco-tampon or keeper is much healthier and more environmentally friendly than a ‘regular’ tampon or sanitary towel, so I would like to buy one, but which one should I take exactly? The silicone keeper or the caoutchoux keeper? What exactly is the difference between the two? Is it also true that you can clean it with your own (sterile?) urine in case there is no sink?

Thanks in advance!