a lot of the negative reviews i've seen come from people who don't know what they are doing. they end up over-oiling the filter and the excess gets on sensors within their intake and causes havoc. Lots of other blow-hards that just start spouting BS about them for who knows what reason!
I've personally run K&N on several vehicles and never had a problem. they are proven to flow better and increase power, although you won't really see/feel that. Engineering explained had a good video comparing dirty, clean, aftermarket, and K&N filters and it was around a 2% gain vs a clean oem filter on his crosstrek.
As said above, the best part is not having to buy another filter! What i do is keep the stock filter around and when it comes time to clean i throw it in the car, clean out the k&n really well and let it sit and fully air dry for 24hrs......if you don't need to drive anywhere you don't need to swap filters obviously, but i'm always on the go! Then instead of the spray oil that usually comes with the cleaning kits, i buy the squeeze bottle of oil and its MUCH easier to put the proper amount of oil on. just run it along each pleat and its really hard to over-oil.
'19 ES Base. Lava Orange 6mt
'17 Santa Fe XL Luxury