I bloody HATE it when people sing from any sort of lyric sheet. If you don't know the words, what are you doing performing (and in my case for money) in front of an audience?
When playing keys on stage, I use a tablet (10" Samsung Galaxy) in a Tiger tablet holder on an old mic stand. I need it for all the different keyboard settings, not for the lyrics, but the audience don't know that. 🙄
I make a point of having the stand at least 45 degrees to my left, 90 degrees if I can, so that the tablet is out of my sightline most of the time that I'm playing, but a quick glance to my left will remind me of what patch is coming up in two bars.
If I was to use the tablet to remind me of the lyrics (never, damn you, NEVER!) I would do the same. Out of the sightline, but available in a hurry in a genuine emergency.