I don’t have an upgrade, so the HM7000 system was by far the easiest and cheapest way. The number of functions on a multimaus are more limited, and for sound don’t give the type. Just a gimmick, but nice to have. Changing locos is also easier. I have about 30 chipped locos, when I only run a couple on the layout, it’s very easy with HM7000, you disable all the others, so switching is child’s play.
If I’m running a non-sound loco alone, I sometimes use the multimaus, still prefer the knob above the virtual slide bar or speedbuttons. For programming the TXS decoders, I also prefer the app, you can see all the CV’s in a blink, and can just write them on the track (apart from CV1). And that’s handy since I have PIKO A-rails.
The app isn’t too bad, especially on IOS (don’t like it on Android, but could be my old phone too). How do you compare it to the z21 app?