As it is advertised, it is a very soft eraser. It even broke where the paper wrapper meets the eraser.
Because it is so soft it does not harm the paper, but it leaves a lot of residue behind it. This is my biggest complaint. I do not recommend it for "home" use as you will go through a lot of trouble to keep the carpets eraser shavings free.
And I do not compare it with the so-called dust-free erasers, but with regular ones.
It erases very well the polymer leads HB and 2B. The paper is clean after, with no smudges and no marks of previous writing.
On the softer leads 4B, 6B it left behind a very faint trace of lead, but most likely it is not noticeable if you are not looking for it.
The charcoal and colored pencil were not erased completely.
The price is very good. The S20 is about 30% cheaper than Faber Castell dust free small eraser, and half the price of the full dust-free eraser. But because it is so soft and brittle I think it should be compared with the small one in terms of longevity.
The 36R is even cheaper, about 3 times cheaper than the Faber Castell dust free small eraser.
In conclusion, Factis are not bad products, but definitely, have some issues. If you like to do Sudoku before bad time, definitely do not buy the S20.