In terms of quality, I think it's pretty even between the big three of PGYTech, Freewell and PolarPro. ND filters from all three brands will get the job done.
PGYTech and Freewell are comparably priced for most countries but PolarPro is significantly more expensive than the other two. Where I am (China), PGYTech is the cheapest and most convenient (Freewell has minimum order requirements for free delivery), so I chose PGYTech.
Here is my first footage with ND16 from Sunny Life (chinese) on my Mavic Mini - The sky was grey, no direct sun light - i did not use any colour grading ot filters -hope you like it!
I find it usefull since in Algarve - Portugal we have a super bright sky.
The best ND/PL filters for the Mini 2 are made by Tiffen. They have 80 years experience making filters for professionals, which should speak volumes. We use the Tiffen set for our Mini 2.