I bought this before the filter offer was available so these comments refer to the lens only. I ordered on Thursday afternoon and the lens was delivered first thing on Monday, so top marks for service. In the following five days I have taken 1200 photographs of all kinds to give the lens a good work-out.
Wide open and at 300mm the lens is acceptably sharp for 6"X4"s but needs to be stopped down/pulled in for larger images. Contrast is good. The autofocus is good in well-lit contrasty situations, but tends to "hunt" in less ideal circumstance. The auto-focus is clearly audible 20 feet away so wild-life enthusiasts will need to focus manually.
Macro claims are a bit optimistic! I'm a disabled, wheel-chair user and a "normal" macro lens isn't always feasible for me. That said, my old Sigma 90mm macro easily out-performs this. This is useful only if you would otherwise miss the shot and to call it a macro is a bit optimistic.
The other thing that concerns me is build quality. It feels a bit plasticky and I can't see it lasting a long time (I have a 36 years old PrinzGalaxy that is still in pristine condition).
I'd give this a conditional thumbs up. If you're on a budget and need a decent telephoto lens it's fine. If you've got pots of money and know a good hernia-transplant clinic save up for a Nikkor.
Three months later and my respect for this lens has grown. It is the lens I have on the camera most often and it compares well with my Nikon 18-200mm (cost three times as much) and the much hyped Nikon 50mm f1.8.
At the price, it's a steal! I'm just glad it's not a Nikon because I wouldn't be able to afford it!