In recent years, Lafuma has adopted the European standard test methodology for the sleeping bag temperature recommendations.Independent (qualified) test laboratories conduct the tests using heated copper "bodies" in accordance with the detailed procedures of standard EN 13537.

In the last few years, many US manufacturers have also adopted this standard for setting the temperature ratings, thus eliminating the "lie game" by the low cost manufacturers who adopt the standardized rating system. I think even Slumberjack bags - famous for weight and temperature rating lies in the past, will go with the new system. Maybe not, because the audience they sell to is not sophisticated, but rather "economically focused" on low cost, and are more often car campers rather than backpackers.

Yes, it was true in the past (before EN 13537) that Lafuma temp ratings were "optimistic", but when REI adopted the EN system, they had to change temperature ratings or redesign the bags they were selling, for one example. There are others.

Lafuma went to EN standards in about 2008 ( my "guest" bag is a January 2008 Lafuma rated to the new standards at 30*F - and nobody has complained)

I'm not selling you on Lafuma. I am selling you on understanding today's temperature ratings. Ask about the certification of the temperature rating of any bag you want to buy. If it isn't EN 13537, then think about the purchase and try to do more research on the specific manufacturer.