The Penzel-Mueller clarinet was certainly a pinnacle in clarinet production in the USA. Gary Kern has started a web site specially for this brand:
Penzel-Mueller fans, owners and collectors, please sign up!

The circa-1949 catalog PDF attached below shows the following models:

Super Brilliante, listing at $300
Brilliante: $250
Artist: $231.50
Empire: $199
Bel Canto: $179.50

The Penzel Pacemaker might have been made by Penzel-Mueller or might have been after the company closed. Because Mueller is not listed, I have given it a separate page.
There were some clarinets made in cooperation between Penzel-Mueller and Pruefer. See one here.

These pictures show a P-M with special keys for forked fingerings, articulated C#/G# and the left Ab/Eb pinkie key.