After some research I came across the HQ switch. It is robust, has two DVI inputs, a DVI output, and a mechanical switch, which has been operated in recent months hundreds of times and has always reliably switched between two PC's.
An external power supply is not required for the device. Cables are not included; it is recommended that the use of highly screened and fully-wired DVI cable.
I run both PC's in Full HD mode (1920 x 1080), and a Qualtitätsverlust through the use of the switch I could not tell.
One must be sure to think about how you additional mouse and keyboard between two PC's switches. I have solved, that I am using my old KVM switch for the VGA connectors and simply do not use.
Conclusion for DVI Switcher: Proper performance without sacrificing quality in the presentation (ordinary cable provided).
The device will receive from me a smooth buy recommendation.