Yes the sun is extremely bright and CU2 is designed for indoor use. It can work in outdoor environments with shade/ But direct sun is too much for the LEDs to overcome.
For your question about seeing the moves on the small screen - possibly. We are developing a “carousel” set of views during game play. In some modes there will be a screen that is the board position - so you can view the pending move there. That is something coming out later this year. It can help a bit in the bright sunlight situations.