Rating reflects poor service on behalf of dealer and Sigma Photo.
I'm a primary a landscape photographer, and here in Missouri I often have to deal with overcast skies and purple fringing around foliage. In fact I've been doing a fair amount of film to avoid that problem.
Out of the box I put this lens to the test. Shooting straight into the sun on an overcast day with a walnut and a spruce in the foreground.
Even wide open it's not horrible, by f/4 the PF is pretty much gone. Clean at f/5.6. I'm happy with the performance of this lens.
But a closer examination of the lens revealed some dust inside the front element. So I called the next day requesting an RMA. The dealer has assured me twice that an RMA would be sent and I've received none.
You can order a lens online, but their "email is screwed up." I bought the lens (and three more--all clean) but I'm not buying that excuse.
A call to Sigma Customer Service probably says it all. I'm told that the dust won't affect my photos, and that all lenses and cameras get dust inside. Of course as a customer I draw a distinction between my dust and their dust.
Further, I have a several Canon FD lenses that have no dust inside of the lens, and that's after 20-30 years of use.
Of course this is a chance I took buying online.
My recommendation with regards to Sigma lenses is not to buy them sight unseen. If their QA passes dust in the elements, then you might want to take a sharp eye or a loupe along on your shopping trip.