They are all a waste of money, and the lasers that fit in the chamber are the worst. At best they "MIGHT" get your 1st shot on an 8.5"X11" sheet of paper at 25 yards. After that you still have to adjust your sights and then move to longer ranges.
If you have a bolt rifle you can simply look throught the bore and get closer. I've never found that one would ever save me a single round of ammo or save me 1 minute of time.
With any type of rifle I can have it zeroed at 100 yards with 3, no more 4 shots.