This one is PGYTECH, pretty cheap but serves well as you can see.
I think no need for buying expensive filters and of course you don't need the whole spectrum of them.
The important thing is that the filter is not much heavier than original DJI lens cover glass. Otherwise you can overload the gimball motors.
If you have two ND, let say 4 and 8 (for special effects you can go up over 100), one CP filter and one graduated grey filter (not colored ones) and there you go. You must know that each additional glass over the lens reduces some light that come to the sensor, at best UV filters this is almost unmeasurable but anyway the best colours and sharpness comes with no filters at all. But sometimes, we've spoken about that, you need filters.