I had this lens until recently and not a lot i can add to the existing reviews and feedback
Image quality is excellent but a little behind the Sony 600/4 in the centre, bit worse towards the edges
Focusing speed is good, ahead of the cheaper sony zooms, behind the latest / best primes and the new 100-400
Absolutely anchor of a lens though, either a monopod or tripod option for prolonged use and the framerate limitations are annoying
If Viltrox bought out a 1.4x TC and the next gen of Sony super primes arent cheaper, lighter and have a built in TC like I hope they will i would consider buying it again but most of the time expect I'll use the 100-400/4.5 & 600/6.3 combo