The reference was it’s a basic function. Other then the UI (user interface) for configuring.
Static IP, Reserved IP, Static/Reserved Lease are often used interchangeably. They may be use for the same thing but don’t always necessarily mean the same. Here’s a post from the past I felt explained it well:
Open source firmware has been around since, I believe the days of the Linksys WRT-54G. If it wasn’t safe it wouldn’t have survived and grown.