I've had my K3 and case for an hour, so I haven't a clue on battery drain from the light. I imagine it will be minimal at most, since it's nothing more than tiny LEDs.
The lettering on the graphite frame is perfectly readable for me.
I'm not trying to trash this cover - it's an ingenious idea. It's just the angle of which it shines on the screen is so strong in the top right corner and fades as it goes down the screen. It annoys me. For $60 I was hoping it would be perfect, but it's just not - for me.