Ready-assembled PCB: all components are SMD and already soldered
Open Source: Sofware is open. You can easily modify the source code. The code is shared via GitHub for different use cases (pico balloon, HAB, car, etc.)
Arduino Compatible CPU: Since CPU is Atmega based, you can use Arduino IDE and libraries to programme LightAPRS.
Extendable: Using I2C and SPI pins you can add extra sensors ( and their librarires) to LightAPRS and programme it as you wish.
1 Watt Radio: In fact you don't need 1 Watt radio module for balloon projects but for your other projects you definitely will :)
High Quality GPS: No need to comment :) Ublox is one of the best GPS manufacturers.
Price: LightAPRS is more affordable than any other APRS tracker