Oh my gosh, the putter is such a lifesaver. I've never been a fan of twisting the tiny, super-slim surface of any type of filter. ND filter, CPL filter, diffusion filters, they all lack putters! I'm certainly glad that K&F Concept decided to introduce this into their filters, including this one.Onto the ND functionality itself, this prevents me from having to increase my shutter speed or aperture. It allows me to maintain a shallow depth of field on my subject even in broad daylight. And yes, it also works for landscape photography and other uses, but my main usage has been for taking video of people.If you're familiar with the exposure triangle, you may recognize my situation. Reducing my aperture would remove my shallow depth of field, and increasing my shutter speed would make my subjects motion look weird, it would just look very off. There would be no motion blur, and as a result the image looks unnatural in our eyes. So, this ND filter was perfect for fulfilling that need.Overall, I really do recommend this filter if you're looking at increasing the quality of your videos, and obviously this depends on what you're looking to use it for. If you know that you need an ND filter, don't go with the cheap glass. Go for something like this instead! It'll totally be worth it.

The Reusable K-Cup filter fits my Classic-K perfectly and after one week is working fine.

I have used them before and have been very pleased them. The air filter goes into my 2010 f150

Better milage and power. I track my MPG, and with this filter, I can say with confidence I get at least 1-MPG more on my F-150. Probably slightly more. This will pay for itself in no time. I had this filter on an older V8 Northstar with up to 300K and going strong until the deer crossed my path. That car too got better milage. And you can feel the start up acceleration is better if you're in tune with the machine.

Good filters for the price. Slight warm color cast. Photo without a filter was shot at 1/2500 f2.8. The other image is 30 seconds f11, ND1000.Overall I am happy with my purchase. If I were to need to use an ND filter more often, I would have bought something more expensive. But these suit my needs just fine.

Second filter I bought, did not have time to clean the first filter I bought. First filter lasted 11 years and 150K miles. 5 minute install.

Noticed a smother engine performance with K&N filter

The K&N drop-in filter is an exact replacement to the stock OEM filter for my 2012 Ford Focus hatchback. Most difficult part was to line up the filter so that the airbox cover fits over the lip of the filter. Once installed, throttle response was better. I have the 6 speed dual-clutch transmission and the K&N seems to smooth the initial start of the car from rest. I am still gathering data to determine if the K&N filter actually increase MPGs and by how much. If previous K&N filter experience that I have on a 2007 Mazda 5 and a 2000 Saab 9-5 Aero wagon is an indicator, then I will see better gas mileage (1-3 MPGs) with additional throttle response and horsepower.