I thought that the entire cast of singers was superb, with no weak links anywhere. The fact that they sang in German vs. the normal Italian should pose little problem for English-speaking audiences, since the subtitles are easy to read. As a historic performance, it is top-notch. However, the fact that it is in black and white, rather than in color, with less than perfect video quality might be a problem for some.
There are other, more recent, but still vintage, performances in color and good audio quality available at reasonable cost (e.g., the Met recording with Paul Plishka, Mirella Freni, and Marilyn Horne). Personally, I preferred Horne as Mrs. Quickly, but there is nothing wrong with Elisabeth Hongen's portrayal of the character.
It's not often that one gets a cast with all of the singers having such good quality and tightly focused voices. A decision on whether to buy this DVD will therefore probably be decided by how devoted one is to adding to one's collection some great singers of the past, such as Elisabeth Hongen, Otto Edelmann, and Graziella Sciutti.