I've used one to reship pharmaceuticals from an online pharmacy that won't deliver to Canada. It worked once and then the second time they blocked the shipment as they realized what was in it. I was still able to have it sent to a different US address.
I've thought about using them for SN. It might work / might not. They let you fill out the customs declaration yourself so it's likely to make it through customs. The main risk is if reshipper realizes that it's a prohibited item and prevents you from reshipping internationally. However SN is cheap so it wouldn't be a huge loss really.