Does anyone have experience with an Ok to Wake type clock?

(a clock that changes color to indicate that it's ok for your kiddo to get out of bed)

We are considering this for our almost 3 year old. She's in a "big kid" bed, but will not stop trying to get out of her room multiple times a night. We have a door monkey lock (to keep her safely in her room), but I think the clock would be awesome. I'd love to hear your experiences.

Links to ones you love as a bonus?