I don't think it is one of the NDA things, but I'm also not sure. If you downloaded the beta app that was made available to everyone with iOS back around Dec/Jan 2015/16, you can see if it shows the hap for the App layer. If it does, that would show you the key combo. If any other tester knows if this is NOT one of the NDA items, they could also pass it on.
Near as I can tell, it does exactly the same thing as command-tab (or add shift to get it to move backwards). Personal preference would determine what you like to do the most, but one advantage with the WT method is that they have a command you can put any place you want and could, thusly, not require any combo keys. Or maybe a simpler one.
It seems to work on Mac and iPad. The iPhone doesn't seem to allow you to bring up a list of programs the way the other two do.
Going back to personal preferences, it also depends on what you are comparing. For example, "command" on an Apple keyboard is out of the way on the bottom - which is uncomfortable for me and I certainly am leaving the home position. So doing it on the TB, once you get used to the chords, is easier for the same keystroke, whether selecting command/tab on the TB or doing the special app layer method. But if I decide I have a place I can put it that won't cause problems with something else, I could conceivably put it someplace really convenient that doesn't require a chord.
Also, remember that normally if you are moving from mac to ipad, they will be in different jump slot - and each jump slot can have it's own layout.
To give an example, I think the "Home" key on the TB doesn't do anything on a Mac (been a long time since I looked at default key maps so I'm not sure this is still the case, but it was with my setup. This key is just to the left of the A key, so easy to get to. If I wanted, I could put the "next app" there and only have to hit that one key by itself. And I guess I could put "previous app" on the same key, but on the green layer. Green layer is really easy.
However, I belief that Home key on iOS takes you back to the home screen, so you may want a different approach there. Or you could change the normal Home usage on iOS to be moved to green/right shift/home.
One of the fun things with the TB is figuring out what the best customizations are for you personally.
An example for me was the fact that I simply almost never use the curly brackets, but I don't want to lose them completely. I also found that I was also often doing something on my computer, but with a mouse (game) and would want to "undo". Easy to do with one hand, but I wanted it to be even easier (less stretch). So I replaced one of the curly brackets with command undo. I replaced the other one with a paste command that is just for one hand use. I think I put the curly brackets on the green/shift layer, but I'd have to double check. Like I said, I don't use them.