Once I learned that I could download tuning apps to my iPhone, I purchased several of them. Most of them were free. iStroboSoft is not. But it is by far the best of the iPhone apps that I have tried. I like the interface and the accuracy. And if you want to isolate the instrument you are tuning, you have the option of purchasing a special adapter to use with a 1/4" phone plug. I've checked it against my StroboPLUS HD, which I also recently purchased, and find that it is just as accurate. I like the idea that you can download special temperaments and "sweeteners" to use with your favorite instruments.
I'm not new to Strobe tuners, by any means. During the 1960's, I tuned accordions, pianos and fretted instruments with a Conn Strobo Tuner. I used a Peterson "blue box" to tune my father's harpsichord. That tuner went with the harpsichord when I donated it to a museum. I'm still using Peterson products on just about anything you could imagine. In fact, I actually used iStroboSoft to correct a mis-tuned tuning fork!