Note after the most recent update, many of the double tap apps no longer work because the physical/digital field is no longer being populated. Use of these smartapps was always somewhat iffy. Not all switches supported them and if the message was passed through a repeater the distinction would be lost. This is why some people said that the double tap smart apps worked great and other people said they never could get them to work. Even if the people had exactly the same devices, just a slight change in network configuration might cause one group to fail.
As of 2016 there are now a couple of different model switches which capture the double tap action at the switch itself and then use “central scene” command to send a specific code to the hub to tell it that a double tap was performed. These are much more reliable than the old software only methods. As of this writing, the central scene method is available on both the homeseer switches and the newest is zwave plus GE switches, as well as some smaller brands. So if anyone is interested in double tap functionality specifically, I would look for one where it is the switch itself that does it, rather than using a double tap Smartapp. 