Worked with these for 8 years now. For the most part, they are solid and reliable. As with any electronics, moisture from condensation can do some damage to soldered components and rust/corrosion on battery holder. Make sure to seal air passages from interior to exterior of door within the hardware.
Range is ok if in straight line down a hall or open area, can go through a block wall. Will need some DB Gain remote Omni or directional antennas if going around corners over 60 ft or long straight line distances. Use test kit to determine. Had to use Schlage RB relay boards(dry outputs) in PIMS to make Brivo compatible.
Actually like AD 400 better than some later models. Now have improved spring cages and battery holders. Only a few have had components go bad due to something other than moisture. Good troubleshooting guide. Expensive though.