Pretty darn reliable. Have wireguard setup to my node and zeus runs as smooth as if it were connecting to my node from the local network (wireguard is pretty cool). Have sent sats in the range of millions and had no trouble, but depends on how well connected you are to other nodes, something that you don't have to bother about when using services like WoS. WoS also charges high fees is what I have heard. Essentially you are trading high fees and custodianship for ease of use and no maintenance.