Maj; Most master plumbers have the experience to do what is required to clear a stoppage in a bathtub.
It is my understanding that there are some indiduals that may not be experienced in the service aspect of our Industry.
If an unschooled person was to run a cable and cuter through the waste and overflow and rupture an old lead drum trap or waste branch, I would be deluged with letters berating my very sensitive personage for making such an error in judgement.
Whether it seems a professional approach or not
may be a valid issue with those who do not service older buildings that have fragile old lead piping that can easily be damaged with too vigorous a method.
I use a 6.25 hp Rigid Wet-Dry for doing this type of work and find that does a fantastic job with out creating any additional woes for an already anxious owner.
To date I have had so problems with chemicals or electricity from using my vac-technique to clear stoppages in sink and lav traps and waste arms as well.