I used the mobile app last year. It is ok, I use when at work etc.
It is a good secondary source, I use in a non real time manner.
Between issues or events at work I read the rundown.I think the scoring is RT, but I controll the scroll or lap by lap note reading.
There is usually some updated text every lap or other lap. Who is passing cars, who is falling back , bad and good pit stop info etc.
Nothing like watching on the tv, but you can use the scoring on the app and zoom out the banner on the set if you prefer.
Thats my POV using a Galaxy Note 2 phone.
The Apps are listed as free, it may change after the seasons start.
I unload the Apps after Homestead and reload for Daytona. I think there was a cost last year.
I will load both next week and keep the one I like best.