You’ve opened Pandora’s box 
I have an M2P and think filters are essential but some of the other members don’t agree so fair warning in case you get some comments from the filter nudists!
Started off with a set of 6 x Freewell PL filters - thought they were great. Broke my ND4 in a freak fog incident last year and having won the Treasure hunt last year, spent my winnings on a set of PGYTech filters which seem great too.
PL Filters screwed up several attempts to get smooth pano’s as some filters seem to mess up the stitching. See post where I asked about this