There is, hilariously, nothing about what people liked about the Witchfinders in the email, but they did have a newsletter which had the following gems:
Jodie Whittaker as the 13th Doctor has been warmly received in the title role. Graham is also highly rated, being named by one viewer as “the standout character of this season”. Viewers are generally enjoying the mix of both historical and futuristic storylines across episodes. The historic third episode Rosa has been described as “a stunning and emotional glimpse into the past…it was beautiful television”.
Plus they apologised a little about the repetition in the Doctor Who surveys, though they tried to spin it as consistency, and how the almost real time feedback helps them understand the performance of the series.
(Though since I keep track... the first three had questions about the core cast and Whittaker as the Doctor, but not the rest.)
( Also, I did rewatch the episode, so bonus bits I picked up from this episode will be included. )