One problem I have experienced with the button method is door interference with the retracting gear. Because the door looses pressure to the "open" side as soon as the main valve moves, air loads can cause the door to close slightly and contact the retracting gear. This has only happened to me with certain doors on certain jets and it can sometimes be corrected by tightening the hinges on the door, making them less likely to blow closed.

In other cases, such as my Rafale with it's 5 sequencing gear doors, it's easier to just use two valves and an electronic sequencer like the Mini Hobby. Plus I like the ablility to manually open the doors and/or retract the gear any time I want.

Craig