The pass will only work on a smartphone and not any other device - not even a tablet.
And it will get you only five of the eleven Sports channels - Sky Sports Premier League, Sky Sports Action, Sky Sports Arena, Sky Sports Racing and Sky Sports News.
Within these limitations, yes it will work and yes it will be free.
It might be better if NowTV could detect your Mobile pass when you tried to access the other six Sports channels, or tried to use a device other than a smartphone, and give you a message accordingly, but it seems you just get told you need to subscribe for a new pass in all those cases.
If my posting answered your question, please click ‘Accept Answer’. If you liked my posting, please click ‘Thanks’. If you disagree with my posting, say so below, and I will see if I need to mend my ways 🙂