I'll let others split the pin heads of differences between the two product lines WRT our building, although I do have both opinions and some heart strings...
Instead I'll tell you the story of why Rey uses Manganese and Col has Chromium. In the early 20th century each country's industry found it cheaper to use the materials that were provided by their lands be they home or colonized. England held South African colonies where Magnanese was mined. Italy had access to chromium mines. I have also been told that Magnanese favors mechanical hardening during its processing. Chromium supposedly likes/enhances heat treating. Hence why Rey used more mechanical processes and Col relied more on heat treating to achieve final specs.
Is this an old framebuilder's tale? It was an old builder who told this to me, so I guess so
I've considered all the steel tube brands to be pretty much the same WRT the raw steel's characteristics. Most all my choices are made with diameter, wall, butt profile and availability as the primary drivers. Andy