This was quicker than I thought: Amazon was not supposed to deliver the Hue Smart Button until November, but now it happened very quickly. And I have learned from Signify sources: Amazon, after all an exclusive sales partner for the start, will also apply the correct price of 19.99 Euro for the Hue Smart Button soon.
Different form factor than the Hue dimmer switch
Thus, the Smart Button is 5 euros cheaper than the Hue dimmer switch, at least as far as the recommended retail price is concerned. And even though the basic functions with on/off and dimming are similar, you still get a completely different form factor.
The Hue Smart Button is only slightly larger than a 2 Euro coin. Thanks to its magnetic bottom it easily sticks to the fridge or other magnetic surfaces. Alternatively, there is a small magnetic adhesive pad that can be mounted on any smooth surface.
Hue Smart Button fits on an empty switch box
In addition, the Philips Hue dimmer switch comes with a 7.6 x 7.6 cm base plate that is either glued or screwed on. A plus: the four drill holes fit exactly into the holes of a standard flush-mounted socket. However, the light switch protruding from the wall would have to be removed to screw on the Smart Button's plate.
I will give the Philips Hue Smart Button a go in everyday life in the next few days and then get back to you with more impressions about setup and handling. If there is anything special on your mind that I should take a closer look at, let me know in the comments.