If they add battery backup, it would be worth 5 stars, but my power is not that reliable.

some reliability issues - one unit completely died about a week ago - no power when plugged in.

You won't oversleep when the power dips on a cold winter night and you loose power for a few seconds.

The unit I bought was defective, losing power for no reason several times a day.

If you lose power during the night and it resumes while you're sleeping, Then forget about waking up on time

Bad R&D from Sony