Lol, I literally just did, there is no carve out for broadcasting the transaction as well as using their service. So, I mean what are you referring to exactly.

It pays 2x fees at a given time and is primarily for non-standard transactions with guarenteed block time within a day. Relaying those don't happen because policy. Someone could submit to another miner and nothing stops them but right now there aren't many offering slipstream like services.