Only problem I had festellen.
The ringing frequency works with 20Hz, which in Germany 25Hz are standardized.
This makes the device partially incompatible with German products. This includes some old Siemens Gigaset phones or telecoms. The phones will ring just not when they are called.
The support is very fast and friendly. We have analyzed the problem and created a feature request. In upcoming firmware it will probably be an additional setting for ringing frequency.
Ansonnsten decent product if the devices are compatible.