I knew that the 35 mm Rondinax tank had also been marketed by Leica (shades of Leica’s present strategy of badging Panasonic cameras) but I didn’t know when that was. I found the answer on a French website*. The collaboration began in 1949 (Leica Code TEOOH) and continued until 1954, except in U.S.A. where it continued until 1961.
That obviously explains why more Leitz-badged Rondinaxes are seen on the US eBay site.
The Leitz-badged version was named as the Rondinax 35. It appears that this designation covered both the Agfa Rondinax 35 and the 35U, the latter with the knob to open Leica and Contax cassettes. I have seen photographs of tanks marked Agfa Rondinax 35 and they lack the special knob for opening labyrinthine cassettes. In fact, the lid of the Rondinax 35 appears to be identical to the lid of the Essex 35. But that raises another question: when did the Agfa Rondinax 35U replace the 35? Was it soon after Leica came on board (in order to enable opening of the special Leica cassette) or earlier?