Yes, it is. But what I would like to see is that I manually adjust the brightness to a level I like, then hit the auto button, and within the range of control, expect the phone to maintain that level in varying lighting conditions.
OTOH, the brightness level I like in the day may be too bright for night. But it's all relative, and that's what I'm looking for... is to keep the screen brightness at the same relative level for varying external light conditions.
What I find is that the autobrightness setting is generally too dim for my eyes. So either I live with it or go to manual mode.. which going from dark to light, becomes difficult to find the control. Right now in a bright, daylit room, regardless where I set the manual slider, when I touch the auto button, it dims to the lowest level.
I used Lux for a good while until the 4.3 update broke it. I had some nice custom profiles that worked pretty well for me.