DJI drones operate under two major sets of regulations:
FCC (for US, Canada and a few other places)
CE (for Europe and most other places).
 
Because CE regulations are much stricter, the drone needs to turn its radios way down, from an FCC allowed noise of 26dB on 5.8Ghz all the way down to 14dB for CE, which is a very big difference given the logarithmic nature of the dB scale.
For Ocusync 2.0 drones (Air 2, Mini 2, Mavic 2) for example, this drops the maximum range from 10km to 6km and offers much less stability at close distances when going behind obstacles like trees or houses or when flying in area with high interference. The 5.8Ghz band (mostly used in urban environments) is even more limited than the difference in maximum range (obtained in 2.4Ghz) would suggest.
The FCC mod allows the drone to bypass these restrictions and turn its radios to full power.
Furthermore, the FCC mode enables frequencies that are disabled in certain countries (e.g. 5.8Ghz is re-enabled in Russia and Israel).
If you are already flying in an FCC country (e.g. U.S. / Canada), this mod won't do anything for you as your drone is already transmitting at full power. The only reason to get it would be if you're planning to travel abroad.
 
Please be aware that turning up transmission power without specific permission from the competent authorities as well as flying outside of VLOS is illegal in most places. We encourage you to always follow your local laws and regulations.
 
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Supported controllers:
DJI RC2