SonyAlphablog posted the worldwide first review of the Tamron 18-300 for Sony. He concludes:
The Tamron 18-300mm F/3.5-6.3 Di III-A VC VXD (749 euros) is a pleasant surprise. Yes it is heavy , yes it is very long , yes the aperture is quite small but image quality is there with very good sharpness , some very nice color rendition and smooth background blur when used at close distance.
It is much better than any of the numerous 18-200mm available , than the Sony E 55-210mm F4.5-6.3 OSS. It is simply the best all in zoom zoom for Sony E mount.
It will be ideal for travelers that want to take only one zoom with them and shoot from landscape, street, portrait to animals photography
The zoom is equipped with image stabilisation which is a big plus for most Sony APSC cameras (except A6500 and A6600 that have sensor stabilisation).
AF is quick and precise in good lightning conditions but don’t except miracle with an aperture of 6.3 at 300mm in low light, ISO will climb very fast.
For video if you do static plan it delivers very good results but the zoom ring is very stiff and you can’t get a smooth zooming while filming
Recommended for travelers who want a quality mega zoom