We had an outdoor gig over the weekend. I learned the hard way that my GNX 3000 is unusable in direct sunlight. Even if you deliberately cast a shadow over the display, it is simply not bright enough to see. At all. I ended up just disconnecting it. Fortunately, I don't use it for much anyway.
On the other hand, my Vocalist Live 4 was readable. Barely, but it was sufficiently legible that I could use it.