I was there last night. It was very bright- the work/house lights are on during the pre-show pie. I was upstairs, in the second (last) row (there are only 2 rows upstairs). I had a seat downstairs during the pie, as there was no table/space to eat upstairs, and then was moved upstairs for the show.
Once the show started, the lighting got a lot darker. I loved it. The view upstairs (especially in the second row) was definitely limited, but most of the action happens by the pie booth & stairs. Despite it being and innovative/immersive/site-specific production, most of the performances felt very standard, particularly the actor playing Sweeney. I thought the actress playing Mrs. Lovett didn't have a very good singing voice, which was jarring compared to the other women in the cast. Betsy Morgan was the stand-out performer of the show. I saw her in First Daughter's Suite, and she continues to shine onstage - she's also pretty visibly pregnant, so I don't know if she'll leave early/need a replacement.
All in all, it was a great night. The house is tiny, and the whole show was very intimate, yet there seemed to be a lot of partial view seats. There was a marriage proposal after curtain call.
Also, the audience has to leave the house during intermission. And programs are given out after the show.