The Sigma 2x EX DG Tele Converter is intended for Canon cameras only. The TC allows photographers to maintain AF throughout the whole range of focal lengths as advertised. Given the f/12.9 maximum aperture, the images produced may not be too spectacular at 500mm.
Nevertheless, they still look adequately bright and color saturation is acceptable. Exposure is generally accurate, although it is somewhat noisy. Image quality is better at 400mm and for best results; it is advisable to mount the camera on a tripod.
Overall, the Sigma 2x EX DG Tele Converter does look solid and the multi-coated elements will resist wear and tear better.