The aesthetic we were going for was more Apollo Guidance Computer, so 7-segment LEDs were perfect. It turned out to also be a great design choice software-wise because the entire rocket originally ran on an atmega328 which had only 2k of RAM; there really wasn't much room for frame buffers. But the state of a 7 segment digit (plus one decimal point) fits perfectly into one byte, so the entire rocket, which was originally 14 8-digit rows, needed only 112 bytes of frame buffer.
By about 2012 we wanted to write more complex software, so I made new revision of the main controller that took an atmega1284, which has a lot more RAM (16K, vs 2K) and program space (128K, vs 32K).
The big retrofit in 2019 went to a 32-bit STM32 which had a hardware floating point unit, making it possible to do fancier animations. The rocket now supports the classic "snake" game.
But still just 7-seg LEDs :)