What is your experience with a break beam photoelectric sensor?

Looking at getting 4-5 break beam sensors with reflectors to trigger a few of my props. The range I'm looking at is just 3'-4'. I read a couple threads on other websites where the sensors may get hot if on for long enough. They might need a couple minutes of "quiet time" to get straightened out in order to not give false readings. Some users had to put tubes over the lenses to narrow the focus. I never used them so I didn't know these problems existed to the extent from what I have read.