Summary: I would recommend this TC only to those who would have the patience to use it properly. Most people would probably be better off with the 1.4x model, which is much easier to use. With a long lens like the Nikon 70-300, the effective focal length can be so great that holding for a sharp image becomes...
Pros: Good magnification; works well; adds little or no softness or distortion
Cons: A bit difficult to use; does not autofocus on many zoom lenses
Excerpt: I use this lens with a Canon 70-300mm lens.The Kenko gives automatic focusing up to about 200mm,but from there to 300mm it does not.One must focus manually in this region-which is no big problem.The teleconverter is well made and has the look of qualityI would recommend it.
Pros: Easily Interchangeable, Fast / accurate auto-focus, Lightweight, Rugged, Strong Construction
Excerpt: I have excellent results with this converter using my Nikon 300 f4 lens, even hand held most of the time. I shoot with a Nikon D3s so I do push the ISO up to keep my shutter speeds over 600. Technique is key with this combo. It doesn't work with my 80-400 over 300mm zoom.
Pros: Consistent Output, Fast / accurate auto-focus
Excerpt: Bought this product to use with a Canon 70-300DO lens for protability in the field. It works well so far and I have tested it on other lenses including 28-135. It AF at all ranges and all the lenses tested. Also on several Canon camera bodies from Pro to a 30D.
Pros: Consistent Output, Durable, Easily Interchangeable, Fast / accurate auto-focus, Lightweight
Excerpt: Physically there were no compatibility issues between the camera body and lens with teleconverter. It performed well when mounted on a tripod with a 300mm lense, provided the subject was not moving. I used it exclusively for two days in familiar settings.
Summary: I am using this with a Nikon 80-200 F2.8 AF-D which makes the lens a 160-400 F5.6 and I have no complaints. I wish Nikon had and auto focus teleconverter that fits this lens, but all their new teleconverters are for AF-S lenses.