1000 thanks Marine!
I just read all this thread and learned many things from you.

Here are my comments and questions:

- I read that the rosin in the Kester 44 is "non-conductive".
Maybe all rosins are non-conductive or mildly conductive... but, isn't it bad for our application? Isn't its electric resistance an issue? Isn't it better to avoid, if unnecessary, the use of rosin flux because of this?
I know that some rosin evaporates with the heat of soldering but what about the residue?

- Kester states that "Flux cored solder wire has a limited shelf life determined by the alloy used in the wire. For alloys containing > 70% lead, the shelf life is two years from date of manufacture. Other alloys have a shelf life of three years from date of manufacture". What happens after these 3 years? and how can we be sure to buy recent solder wire? where do you suggest to buy it online to be sure that it's recent?
I live in Europe and tin/lead wire is forbidden here therefore I must find a trustable source online extra-UE.

- I would suggest to add more videos

- I read that RMA means "rosin mildly activated" while you wrote "rosin medium activated"