Try it and let me know how it works for you. It doesn't change any settings, and can be easily removed. It is designed to get out of the way (disable itself) when overridden. Also, the light sensor is quite sensitive.

I have been continuously using it since I wrote it (about a year), and have carefully tweaked the behaviour to be as intuitive and unobtrusive as possible. I use my tablet day and night, in many situations (I carry my tablet everywhere,) and I rarely touch the lock slider.

Let me know what you think after using it.