Best when separated
The lens delivers the most intense effect when used on a full-frame camera -- I tested it with the Sony A7 II -- when there's a lot of foreground/background separation between the subject, a relatively detailed background and with the aperture wide open at f2.5.
Nice for portraits
It's a snap to get nice background effects for portraits with the lens -- those are sequins in the background (photo is retouched and cropped).
Manual focus only
The one problem with manual focus is that I would have needed three hands to get the balloon to remain still while focusing.
Colors
One of the effects of the lens is to increase contrast, which saturates colors nicely.
No swirl
When there's no detailed background, the lens still produces interesting color and contrast effects as well as vignetting.
Stop it down
As you make the aperture smaller, the effect lessens significantly and becomes a lot less interesting. You still get vignetting, though.
Contouring
It posterizes some flat colors, like the sky.
Lights
The edge distortions swirl lights in interesting ways.
Round highlights
When highlights appear close to the center of the image, the 12-bladed lens aperture delivers lovely round results.
APS-C
There's a lot less of an effect on an APS-C camera, like the Sony A6300 I used to shoot this -- because the combination of the long focal-length lens and smaller sensor decrease the field of view as well as increase the amount of area that's in focus. Still, it can produce nice highlights and smooth out-of-focus areas.
APS-C
Another example of the effect on a smaller-sensor camera, shot at maximum aperture.
Effects on top of effects
You can add an extra layer of creativity by using an in-camera filter, such as Sony's Illustration effect, in conjunction with the lens.
Black and white
Shooting monochrome with the lens is a nice way to deal with low-light situations.
Fringing
The lens' chromatic aberration is one of its charms.
More examples
The rest are just some more photo samples.