I will have to pick some of these up. I have been operating for years using Engine Driver on my Droid 2, Droid 3, Galaxy S2, Galaxy S3, and Galaxy S4 to run my layout. I keep all my old phones specifically to use as throttles. A few more of these wont be bad at all. Makes it easier when friends come over as well and dont have to tote throttles around and instead can just have their phones link to my layout specific router with WiThrottle or Engine Driver.
I thought I would miss the knob but after using them for a bit I dont miss it at all. I did "extend" the on screen slider and set it to display one throttle at a time, which makes things easier. I have used the volume buttons as well and they work pretty swift. After using it for so many years I cant think of a reason why I would drop $$$ on a Digitrax throttle, when I already dropped the same amount on a phone that I am no phasing out.