I have all these things on my smartphone too but wanted something I don't need to plug in and will also house my USB sockets. Seemed to work great today. Very happy with it.
Its the same with speedo apps. Once you've verified it against your analogue one, you don't need to look again.
As an aside (and it annoys everyone but no one mentions it) is when you get home with say a quarter of a tank and then set off the next day, it takes an age to get a reading and is highly dependent on level ground. Its hard to know whether you're on the level with road camber all over the place . At least this way I can know what the fuel gauge says is more or less true. It works very well.
Altimeter probably academic.
