The RVLINK is a long range relay for your RVOSD6. It is already included in the 525USD set.
Range: 20- 40km
RVLINK receiver PCB for RVOSD
Male to Male servo cable
RVOSD6 RVLINK Rx module.
USB updater to load new firmware into RVOSD ( if you are buying this RVLINK to add to a older RVOSD6)
Standard R/C receiver with PPM or SBUS output.
2S-4S battery to power the RVLINK transmitter.
More information here: https://www.rangevideo.com/rvosd/