Ok, so I played a bit more with hammerhead, and it seems that its GPS is above average. It was able to get indoor lock near window, where my old Fortuna bluetooth GPS never got anything. (OTOH it was not able to get a fix for hour and half when I tried to use it for real -- and that wood was not that thick).
It took me quite a lot of time to figure out how to make nmea recording to work. Apparently, low level test is required before stuff works. Here's the script:
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