That is the first time I have seen an adjustable RCBO!
Generally if you get a 30mA tester it will show if any RCD/RCBO that is rated from 5-30mA is working OK or not. It is not as precise a test as an electrician can do with the appropriate test equipment to verify the trip-time (usual test at fixed 'fault' current at device's specification, e.g. 30mA) and the trip current (done by slowly ramping up the 'fault' current to see at what point it fires). Any external tester would confirm if it is the RCD that has failed/stuck stuck, or if it is the self-test button that has failed.
The use of 30mA is normal in the UK/Europe for most applications as that is the threshold for 'reversible effects' (i.e. it hurts but you are OK immediately afterwards):
en.wikipedia.org
What RCD/RCBO don't do is limit the shock
current, what they do is limit the
exposure time above a certain current which limits the physiological impact but it still depends on how conductive the event was (e.g. if dry skin contact or wet, etc ,etc). So RCDs are very useful in the prevention of death/injury but are always "additional protection" along with the basic protection of suitable insulation and earthing of metalwork, etc.