Well, I asked around several German experts on German gunmkers, companies and families. As far as we know, Max Meffert was not closely related to the well-known Suhl gunmaking family. Though he claims to come from Suhl, he is not listed among the gunsmithes trained there. Apparently he was a pure dealer who intended to make money on his name. AFAIK he was in business for a rather short time only during the "roaring 1920s". The catalog number "66" from his ad is pure bogus to make people think of an old-established company.
The rifle is a typical product of the post-WW1 Suhl and Zella-Mehlis guntrade. It is built on a cleaned-up ex-military Gewehr98 action. There were no "surplus" M98 actions prior to 1918. The shotgun-type triggerguard is a typical 1920s modification, as the Gew98 and rspecially the smll-ring Kar98 triggerguards are to small for convenient use of a dst. The double-set trigger with it's own housing and V-spring is the typical set from the time. The stock is of standard shape used by all Suhl/Zella-Mehlis makers around WW1. The scope is apparently a reused pre-WW1 one. In the early 1920s Germany was on very hard times economically. Optics were, if available at all, very expensive. So, as after WW2 too, it was quite common to reuse prewar optics. Most ex-sniper scopes survived this way, mounted on hunting rifles.