I get views from Pinterest whenever I pin one of my own items, obviously, but also when I'm pinning a bunch of stuff during a high-traffic time. I have my shop info right in my little bio space, and it does, on occassion. tend to send a bit of traffic my way, but I don't think any of my sales have come from it.
I haven't used Stumble Upon yet, but I know it too has sent traffic my way. Both are free, and Pinterest at least is fun (and addicting!), so I say use them and have fun. Can't hurt, right ;)