I just recently got into this hobby/sport and had gotten a Usmile 250, which by the looks of it is a clone of the Eachine Racer 250. The Usmile came with a GoolRC GS6 controller and the flight controller is a KK2.1.5 mini. But it didn't have any FPV capability. I did purchase a camera and vtx and installed.
But this is about the Eachine Racer 250 FPV RTF that I purchased recently. This has the CC3D controller and I have upgraded it to run with LibrePilot. If anyone has read my previous post under General Discussion you know I had an issue for about 3 days. When I first got the quad, I flew it around in the yard for a short time, just hovering and getting use to the controls on the Eachine I6 controller. A few days later I did the modifications that I had followed on YouTube. I cut the face to allow the camera to tilt up more without having the frame in the way. I also filed the opening in the top carbon fiber plate to allow for the additional tilt. I relocated the vtx to the rear bottom, rotated the fc board 90 degrees so the USB port was to the left looking from the back of the quad. Then upgraded/erased with LibrePilot.
I know I didn't build this, but I have had it apart and back together again several times. Still doing a little tuning on it, but I am just wanting to fly.