I've been using OnSong and an Airturn Firefly for at least 5 years now (same pedal, updated the iPad ). Can't say enough good things about it, for my purposes: lyrics, basic chord info, little reminder notes.
I've assisted many people to get OnSong working for their rigs sending out program changes and doing many of the more advanced functions. Easy peasy as long as you take your time and are methodical about it.
OnSong in Night Mode is, for me, perfect, and worth every penny.
Oh, and the Firefly is only two switches, and remarkably more robust than the plastic construction might at first appear.