The dev had a giveaway of lifetime licenses then changed his mind because of fallen revenue and set those licenses to expire after a year. Nothing was taken from customers who bought the app. I rather did see this happening then service shutting down or implementing a subscription fee instead.

Lifetime license otherwise costs 3$ for up to 5 active devices at the same time, so it's quite cheap. I bought it 4 years ago and used in on about 5 different Android phones, you can remove older unused devices to keep the limit down.

The main difference between this and other solutions or Android Device Manager is functionality to control the device over SMS commands. Because ADM is useless when the device doesn't have internet connectivity. Even when someone takes out your SIM and inserts another, Cerberus notifies you about the new SIM and sends you the number of it, so you can control the device over the new number.