These seem quite rare and the only one listed here went for a pretty fair price. Most of the Jen effects are coming out of Europe so I don’t know how many of these found their way across the pond. Jen of Pescara, Italy was probably the best known Italian pedal manufacturer and used to make the Vox Wah pedals and Tone Benders. The Harmon Booster is apparently an early distortion and Gretsch had a version called the Play Boy. Here is what one looks like at DiscoFreq.