It's really better to manually drain, so that you can see for yourself that each drain was open and the water got out. These easy or single point drains all have one drawback and that is you get rust flakes or other debris in the raw water side, and that can prevent things from draining, it could be rust, sand, etc.
As an alternative an engine with closed cooling can be winterized using one of those winterizing tanks, provided that you rig up a pump(like a bilge pump or livewell pump) to pressurize the flow of antifreeze to the impeller. Gravity flow may not work well enough with an engine mounted impeller. The other option is to use a large tub, and a bilge pump in the tub, with the bilge pump attached to a short 3/4" hose that then goes to the muffs. The tub is set up so that the bilge pump is covered with AF, at all times and also so that it will catch the exhaust flow that comes right under the transom mount. This way the AF gets recirculated and fills the heat exchanger, exhaust manifolds (if not on the closed cooling loop) and impeller. But really once you know where the drains are, its just simpler, less risky, less messy and cheaper to just drain the raw water side.
