In my first training company, we carried Kärcher and Kränzle. I was drilled that whenever possible I should sell a Kränzle. As mentioned above, Kränzle has a lot of brass, Kärcher almost everything is plastic. There were apparently also an incredible number of complaints due to broken plastic screw fittings. Then there is no spare part. At least back then, everything could be replaced with Kränzle.
But that was almost 25 years ago. Maybe something has changed since then.
As far as the floor covering is concerned, I could imagine that it is often the manufacturers being overly cautious. Sort of like "Caution! Risk of burns!" with coffee from MCes. What I actually find problematic are the joints. You can probably quickly "clean them out" with too much steam...