I can't find any electrical or material specs either, but I found one of each in my adapter tray, and it looks to me like the insulation on the Trompeter in the triax connector is much thinner. So I could imagine it having a lower resistance rating between inner shield and outer shield (which isn't even specified on either). The Keithley connector looks a bit better made mechanically to me due to the extra insulation, but I'm not sure if that would be worth the price premium to me. See attached pics (Keithley on the left, Trompeter on the right).
If you want me to do any measurements, PM me in two weeks or so.