In principle it is a nice, simple effective device. However, upon arrival the frequency range was way off the scaling: at 100 Hz setting a minimum of 16 Hz, below that no output at all, and a maximum frequency of 16 kHz at 20 kHz setting.
In order to solve this, I decided to open the signal generator, obviously voiding the warranty. I found that there is a small trimpotmeter which presets the frequency range, and after some tweaking I came to 19.5 Hz to 23 kHz. The output level is quite constant over the complete frequency range. Nice!
So for those facing an incorrect frequency range: it can be solved without much effort.
For perfectionists: replace the trimpotmeter by a multiturn one...