There are several versions of that one legged Martini extractor. They work well on fully resized cases, marginally on fired cases.

The Martini has poor extraction qualities to start with and needs all the help it can get and two legs are better than one.

Here is a rimless extractor from a Turkish Martini Peabody modified to fire the 7.65 x 53 Mauser.

Note the radius in the relief cut. It is radiused down so as the extractor rotates it doesn't bear on the cartridge and push it off the extractor.

From this angle this looks like a rimmed extractor. This is cut like this to allow the extractor to go up in the extractor groove and be able push against the rim, (Even a rimless cartridge has a rim.)

This extractor has a sliding piece pushed by a small spring held in place by tongue in groove of extractor arms and plate and retained by a small screw in the side. That divot on the side is the slotted screw head,

Hoffman built one similar as did Bob Snapp. This extractor does work. Doesn't increase leverage, but working the lever vigorously will extract cartridges. That is thr trick to good extraction in the Martini, snap the lever open-with vigor!

After the Turkish Martini Peabody's were modified for the rimless 7.65 x 53 Mauser and sent out in the field, they had to be returned for further repair for cracking of the receiver over the hinge pin hole. Attaching a reinforcing plate over that hole solved the problem.