I said most of what I needed to in Part 1 of this review. This article gives you a few more images to look at, since I'm not about to subject the lens to formal testing.
All images on this page were shot at f/4. Though perhaps not exceptional in content or execution, they should illustrate the all-around usefulness of this lens. Just so you know, I've run my usual processing on these photos, including input and output sharpening. There's a little contrast enhancement and the colour of the sky has been boosted in the first picture. Further enhancement could no doubt bring out even more from this lens, but I wanted the pictures to be a useful illustration of the actual lens rendering.
The Vivitar does well both at distance for landscapes and at close focus, an indication that the floating element correction is doing its job. Colour is excellent, contrast very nice and I don't notice distortion -- though I didn't shoot anything rectilinear to really test this.
On the used market this lens sells for quite a range of prices, as is typical of "sleeper" lenses not everyone recognises. If you find it for $100 you've got yourself an amazing deal. The most you need to pay is $300, which I still consider value for money. By the way, it also comes in Nikon and Minolta mounts, though I believe the M42 is in greatest demand.
In case it is still unclear, I heartily recommend this lens. There might be slightly better 28mm options in terms of pure sharpness -- I'm not sure. And there are certainly smaller lenses or those with auto-focus. But you won't find a nicer lens when it comes to handling in the field. I gladly shoot it at f/2.4 and f/4, getting results I am very pleased with.
One final image, this time with creative processing.