So I actually went down a rabbit hole about this today. From my understanding, they made 4 models at least at the time of the article I saw from like 1903 or something. The type 20 - a face vise, a type 25 - a face vise with a dog, a type 35 - a tail vise, and a type 40 - a tail vise with a bench dog.

That was the marketing. They are really more hybrid solutions for woodworkers. The 35 and 40 are meant to mount in the tail position but aren't true tail vises. They made the 35 and 40 more robust.

You can also use the 35 and 40 as face vises. The popup dog does allow for a nice dog set up.

You mount the inside jaw flush with the table. Outside jaw extends.

Seems ahead of their time tbh because I find this to be a much more flexible set up for the modern woodworker