Open question: How to rate Solder grease?

[Kiriakos GR]

The One million dollars question 

How to rate Solder grease? and following question after that .....> Is it flux better than solder grease?  (solder cream = actual Greek description translated to English)

Every time that my metallic case of solder grease  this seems 3/4 empty, I do also wonder if there is newer and better in properties solder grease than the one that I got before several years back.

In past decade I have trust only Made in Germany products ( due old habit of buying quality goods), FELDER and STANNOL.
In the question as .. Does Solder grease should be in accordance of specification ? yes it does and older known one this is DIN EN29454.1  3.1.1.C

DIN EN29454.1  3.1.1.C
flux residues are 100 % water soluble, for joining copper pipes to copper, gunmetal, and brass fittings for hot and cold-water plumbing in accordance with DVGW worksheet GW 2 + GW 7, also suitable for general-purpose soldering work.

Another description of Solder grease this is Soft Flux.

After typing these words so far, I am now a believer that any other Flux this not coming with DIN EN29454.1  3.1.1.C, this is not appropriate for plumber work and such a product this is would be hazardous for public health.

This topic is for electrical and electronic parts soldering in mind, and therefore what we should worry about this is issues causes by Flux mostly when inhaling it..
By assuming that every one is alerted and cautious not inhaling it, lets move to other thoughts.

My experience with Flux specialized for rework, this helped me to become aware that Flux with special properties ( staying in liquid form with out vaporized for specific seconds of time at high temperature), this is result of advanced chemistry and as such this is not a human friendly product.

Therefore and in conclusion, the question of how many flux types should I own? This is up to you to answer.
For practical reasons we do need soft Flux which it does work, and not some fake product.
And finally if you have discover your very own way to rate solder grease ?  Then please share your secret with us