Great place to catch PBS shows they don't put on their PBS Documentaries channel on Amazon, like Austin City Limits. The 125W feeds have no channel logos too so it's less like getting stuff from a TV channel with the usual garbage plastered in the bottom right corner and it's more like getting it from a clean web source.
PBS's "Passport" website through their official website is garbage, so it's a non-contender for anything but a last resort option, I.E. if they don't upload the piece of content you want to Amazon and they never air it on the 125W feed.
PBS Passport streaming service is stereo audio only with low bitrate AAC audio. It has poorly encoded 6 Mbps 1080p H.264 video, vs. the 12 Mbps 1080i H.264 video with up to 5.1 AC-3 audio @ 448 Kbps offered on the 125W feed. The 125W feed is always better quality than PBS Passport streams.
So to sum it up, the quality hierarchy for PBS from best to worst, in descending order:
1) Amazon (23.976 or 25 fps native content - - any dramas, scripted shows, a mixed amount of NOVA and Nature episodes depending on partnerships with the BBC for filming the episode, etc.)
2) 125W satellite feed (29.97 fps native content or content not available on Amazon, like Austin City Limits and most Frontline episodes)
3) PBS passport service.
The only caveat with getting PBS content from Amazon, is that for content which has a native 29.97 framerate, they are de-interlacing it very poorly resulting in frequent ugly combing lines. Curiously, they deinterlace their 23.976 or 25 fps framerate content properly for Amazon, resulting in a very clean 1080p picture free of de-interlacing artifacts. PBS does not have the most competent people working in their tech department. I attached a few pictures from all 3 sources (125, PBS Passport & PBS Documentaries Amazon channel) showing you an example. Look at the letters and the NOVA logo in the corner. The HDTV version from 125W is the only one that looks correct.
This is from the latest NOVA episode, "Nazca Desert Mystery," so PBS's de-interlacing incompetence continues to this day.