Seems like a neat idea for brass, copper etc soldering work.
I would never recommend any flux be added to an electrical joint. The only flux needed is that which is inside resin cored (Multicore) solder, which is the correct solder for electrical / printed circuit board soldering work. The art of soldering is ensure both items are clean and free of grease etc. and the soldering iron is up to full heat and capable of maintining that heat as the work is undertaken. The item here on my site covers this
Soldering
Caution needs to be exercised, as some fluxes contain strong acids and this causes the electrical joint to become high resistance over time and eventually leads to electrical and joint failure. That is why all the flux manufactures advise you to 'wash off flux' from the item once soldering is completed. This of course can't be done with electrical joints!
As for the newer 'Lead Free' solders.. If you're resoldering a joint/component which was originally soldered with the older lead content solder then the answer is to heat the old joint and remove as much of the old solder as is possible (Solder sucker tool or solder wick etc makes this a little easier! ). Then fibre brush or scrape the joint clean before resoldering with the new lead free solder.