Been looking at these also. Spent some time watching / reading reviews and while they hold up well the most common complaint is the "auto brightness" feature. In extreme low-light / no light situations the dot basically either disappears, or shuts off. The unit isn't equipped with an on-off switch. It's turned off by replacing the cover (in essence simulating no light). Not that big a deal I guess for almost all "normal" situations, but in the less than politically correct discussion about defensive use, a dot that doesn't work in low / no light isn't ideal (to say the least).
FWIW.