Hmm, judging from the reviews, this app doesn't sound that great... I think I will stick with Samsung's version for now thanks Nexus
If Samsung just adds motion sensor to the stay function to detect the position of the phone (i.e. when people hold it upright or in landscape) relative to the face/head then it would be nigh perfect.
It won't just track to see your face and eyes. But the position of your phone upright relative to your face (i.e. placed in front of it at a roughish 40-90 degree angle) will also be monitored. For low light, it will see that there is darkness and will simply just monitor the positioning of the phone and keep the screen on for that.
For the odd positions - well, I would love a toggle for the screen to be always on on stock touchwiz but I doubt that will happen so a ROM will definitely be needed.