I also can only attest positive feedback to the Simplex line.
I‘m using a 30mm on a lot of the woodworking tasks I do, one side with the blue „non-marring“ rubber. The second with „superplastic“.
Then for laying stone pavement, I used a 60mm a lot.
Great tools.
But If you can get hold of one, I would suggest to also check out Kukko.
They manufacture basically the same form factors, but with the option of a removable dead-blow element. (Shot filling)
I really like dead blows for a lot of work, but the option to just remove the filling makes the mallet the ultimate design, in my opinion.
Please find a couple of pictures below of the internals of the Halder Simplex vs the Kukko.
The Kukko is the one with green mallet casting and plain wood handle.
In my opinion the Kukko is nicer made. Better design with the removable dead-blow element and also cleaner castings and a much nicer paint job.