I thought the December 23 deadline works as follows:
DJI will be placed on the Covered Entity list if a national security review is not conducted or it fails said review. This is from the 2025 NDAA.
Once added to this list, the FCC will not...
What props is you brother using? It looks like the spark can achieve a 1.9 thrust ratio with standard props. This would certainly limit your angle of flight. Ballparking,around 45deg before losing altitude
Unless I'm mistaken, you can register any drone, including a home-built. There's no database of FCC approved drones connected to the FAA registry system.
Keep in mind that you MUST register any home-built drone over 250g. A system checking drone...