I did a field test with and without the reflectors on the street about 800 feet away and only a few feet off the ground with cars and mailboxes blocking my path. I can't give you quantitative numbers of how far these will increase your signal, however if you keep them directed at the aircraft always while flying then you will get the most out of them. The smoother and cleaner the surface, the better the performance. Take care to not scratch the copper surface.

A quick rub with a salt and vinegar solution cleaned these up well. Mine had a bit of oxidation where presumably a factory worker touched the metal because you could see the fingerprints. These Kuuqa's reflectors came in a nice box and I was surprised about how small and compact it was for storage and travel since they open and close in a clamshell fashion. I wish there were markings on the reflectors to indicate this but a simple arrow UP with a Sharpie solves the problem. I tried initially installing them and couldn't figure out why they wouldn't fit but it was because they only go on one direction. When sliding on notice that one hole is a different shape then the opposite end. Note that these are made only for DJI transmitters with dual antennas, not the earlier single antenna on earlier Phantom models. These reflectors easily slide onto your existing dual antennas on your DJI remote. They are a perfect parabola (or nearly) where the foci is in the perfect location as to maximize your signal. I put the word 'boost' into quotes because these parabolic reflectors do not literally boost the signal strength, but instead refocus the RF signal out and away from you in a more focused signal. I've seen videos out there of people opening up their transmitters, drilling holes all over and adding different gain antennas onto them but this is risky and also obviously voids your warranty. This increased conductivity means more RF energy will go up and out of the antenna and not get trapped wasted it into heat energy. I prefer copper over the aluminum because copper is the nobler of the two metals which means it has less resistance and therefore is more conductive. If you want a way to inexpensively, easily, and effectively 'boost' your DJI drone's signal strength and range then Kuuqa's copper lined parabolic reflectors are the way to go.

Copper reflector photography