It came with the 10 stop glass filter and seems to be pretty great quality. I'm loving using it. Even ordered a 6 stop to go with it. 

The binocular lens is made of glass. Compared with plastic lenses, glass lenses will provide high-quality images. 

First, K&F Concept ND2-ND400 lens filter allows changing shutter speed based on the effect you want with the best sensibility and the same aperture. Second, K&F Concept ND2-ND400 lens filter allows creating a blurred background with a large aperture while the shutter speed remains the same. Third, K&F Concept ND2-ND400 lens filter is designed to prevent overexposure and maintain image purity and quality at the same time. *Like a zoom lens, the variable nd filters are suitable for multiple shooting situations. If you're looking for perfect image quality, a fixed ND filter is recommended. 

This one is high quality materials, and contains both a variable ND filter + a polarizing filter. Also - most variable Nd filters show and “x” pattern when they’re turned to the max, essentially making them useless at full power. This one shows no “x” pattern. I’m happy I bought it! Very high quality and sturdy. 

Unlike a tube it won't effect your focus distance nor effect your quality like a doubler. The lens will have more of an effect than anything else. On my Sony a7, I must be sure to use a full frame lens since the sensor is 35mm size