Soft cups? Tell me about them.

I'm thinking about trying out these soft cups that everyone is talking about. Can you use them while you're active? I'm very active during the day so I'm worried that if I have one in that I'll move a certain way and it will shift or something and leak I don't know. Can you have sex with them in? Can your partner feel the soft cup when you're having sex? How often do you have to change them? What are the pros and cons. Where do you even get them??