Installing custom software is NOT harmful for FC3000 and you will NOT brick your handheld.
There are multiple custom firmware roms that you can install on your FC3000 Retro gaming handheld, but to understand the difference between them, please read glossary first.
Name Definition clean
Firmware does not include game ROMS. You can use it as a base for your custom games installation complete
Firmware may include preinstalled games. jutley
Old developer of custom firmware neotendo
Developer of custom firmware (recommended to use any custom firmware's based on @neotendo) opendingux
Group of amazing guys releasing custom firmware based on @neotendo and @jutleys firmware bob
Another guy releasing custom firmware for FC3000 gramer
And another guy releasing custom firmware rom with preinstalled games polgamer
Custom firmware that included preinstalled polish games
Each firmware can be released for specific FC3000 model.
Version Difference FC3000 V1 TFT
FC3000 with 8 emulators and TFT display FC3000 V1 IPS
FC3000 with 8 emulators and IPS display FC3000 V2 TFT
FC3000 with 10 emulators and TFT display FC3000 V2 IPS
FC3000 with 10 emulators and IPS display
When the custom firmware is based on neotendo
firmware, you can easily use MakeMyFC3000 tool to patch it for different FC3000 model.