They are not as good as made out.
I have a powerful steam cleaner, the sort that sits on the floor with a tube and handle with various attachments. In other words, it looks like a non-upright vacuum cleaner.
It does NOT clean grease off cookers like they show in demos, I think they are only using HP sauce as their "grease" LOL.
I used it to clean some mould off bathroom tiles, it worked but was slow. But it was also unpleasant, as the whole room became filled with steam, you could hardly see what you were doing, and it was therefore hot and sweaty work.
I bought it from QVC about 10 years ago, and have only used it about 3 times, it was a disappointing buy. At that time, I think they had only just come out for domestic use so were rare, now you can get them everywhere.