The Geprc cygnet 3 out the box is an awesome quad out the box with awesome flight times about 11-12 minutes on a fresh 4s 850mah battery & with the runcam split onboard its capable of nice 1080 hd jello free footage clear of any props in view... (because to me props in view are like when you have a Freshly washed and waxed car a then a little bird flies by and leaves a turd on your windshield)

I originally added a gps unit through reassigning the pins for the LED pin and the TBS SA pin to act as a RX & Tx pin in betaflight. After testing it out it flew fine, but the onboard R9mm rx was still limited by the stock Stable FC stack /200mw vtx, and since the vtx is part of the stack & attached via header pins, adding a different one would prove to be a difficult task..

Time to get creative so, I emptied my couch & ashtrays and went to coinstar again....looks like daddys got a new Diatone Mamba 405 mini stack from race day quads the ...the best Quad company for your FPV hobby purchases and an Akk 1000mw mini (20x20) vtx that I was able to sneak into my wifes daily flow of amazon prime orders.

The flight controller/esc combo arrived a few days later...and geez if you want a fc stack that will kick your ass and take your lunch money while soldering... this combo will definitely do it....the pads are smaller than a fly's peter after swimming in a ice cold pool and when all was done it definitely put my smoke stopper to use. I still utilized the stock geprc 1206 4500kv motors and extended the wires with racewire from Tiny's LEDs.
The other most frustrating thing in this build was finding correct hardware and trying to cram a run cam split board, big arse akk "minil" VTX, flight controller, 4 in one esc, along with capacitors into this hot dog frame and not having anything short or ground out or having black lines in the video feed.

Then topped of with a BN-220 gps module doubled sided taped & ziptied onto the forward part of the quad above the camera. Im currently in works on redesigning the original rear 3d printed tpu parts that sit in the frame to include a gps tray along with a crossfire / r9mm antenna mount and will release it on thingiverse for folks to modify to their liking.

Tested the quad on stock betaflight pids with the gps module enabled and it seems to fly ok but definitely needs more tuning as it seems this FC is quite sensitive to vibration noise. Did an initial 9 minute flight with a 4s 850 battery and  14 minute flight with beefy  Zohd Lionpack 4s 3500mah with a Xt60 -> Xt30 connector adapter. That pack is good for long (slow ) flight range but you cannot perform any acro manuevers as the amp draw is too much and this thing weighs almost double the regular 4s 850 coming in at around 212gr.