We bought our first AC401 2 years ago, and recently added a second one for our new baby. Still use my first monitor for my now 2-year old until she will move to her toddler bed.
These monitors are fantastic and allow me to sleep without worrying about baby's breathing. My little girl had a cold and stuffy nose when she was only 1 week old, but having the movement/breathing detectors in place, I knew an alarm would go off if something went wrong with her breathing.
Things we like:
* it has 2 sensor pads, so less risk of a false alarm. We've had 2 false alarms over 2 years, and my baby was lying on her side at the very end of the bed. Also the sensitivity is adjustable to minimise the possibility of a false alarm.
* rechargeable parents unit, so no need to worry about (cost of constantly replacing) batteries
* Various options available, such as a 'tic' sound, out of range indicator, movement or sound only monitor, etc.
* Temperature is clearly displayed, makes it easy for me to see which grobag to use.
* Has a soft blue night light which I use for night feedings
* Never had any static of interference which can be a problem with some monitors
Overall, we are very happy with our angelcare monitors, and I wouldn't be able to sleep soundly without them. Highly recommended for peace of mind when your little one is sleeping :-)