Oil drain valves are like liver and onions.... you either love them or hate them. I am not trying to talk anyone into using a drain valve, just wanted to let you know what parts to buy. I have used these valves for years because they make the oil change so easy. I would think that to get most of the dirty oil out of your car the most important factor would be to make sure that the engine is warmed up and the oil is hot before draining. The drain valve keeps you from having to remove the hot drain plug while the hot oil is splashing around. You just open the valve.
However you do it... keep that oil clean!