I bought a few of these to round out my Mobilchoke arsenal. MDS stands for "Mechanica del Sarca", and is a subsidiary of Beretta. They make choke tubes, magazines and various parts for Beretta.http://www.sarca.it/default.htm
Their Modified and tighter chokes are marked for Lead Only, but the more open ones have steel rating on them too. They have a very complete range of constrictions as well.
I have only used my Light Modified and it seemed fine, although I have not patterned it.
The wrench notches seemed a little tight for my Berretta Mobilchoke wrench, but for the price it would hard to go wrong, try em out.