Perhaps it varied from unit to unit, but as I posted before, with v1.0 firmware, there was zero objective/subjective difference. After upgrading MCU and XMOS firmware, filter selection works as advertised.
~For now, Linear Fast is my favorite.~ 
Update: I’ve done more listening, and subjectively speaking, I actually prefer Hybrid Fast. According to my measurements, high frequencies are a little rolled off compared to the others, but I don’t think that explains what I’m hearing.
Perhaps it’s a time-domain thing? When I zoom in to the impulse response, I do see less pre-ringing for Hybrid Fast than the other six options.
It’s difficult to believe that I can hear a half ms or so of pre-ringing, but this sort of thing does not happen nature, so perhaps this explains my preference. Surprising since, looking at the frequency response, I was sure that I’d prefer the sound of Linear Fast.
For those who have the latest MCU and Firmware v1.2 (or later), I’m interested in any filter preferences you may have discovered.