The second fight in the upper tier had our party (investigator, mesmerist, sorceror, paladin, and swashbuckler) legitimately scared, and without introducing any odd new dynamics to do so, just a ruthless and effective enemy strategy.
Placing a moral quandry at the end allows for the possibility of more RP at the table as the party has to make a tough decision.
I played this scenario with four players, one fighter with average CHA, one sorceror, one paladin who had a +14 to diplomacy, and one vigilante with +12 to diplomacy. I'll note that this was in tier 1-2. In any reasonable social scenario, this party should have been able to handle it. Instead, due to the peculiar mechanics in the scenario we could barely achieve the primary success condition despite multiple extremely high diplomacy rolls. It seems that the scenario was falsely advertised as a social encounter and then negated the skills of the good social characters.
I just ran this last night in high tier, and the players loved it! I had just enough time to squeeze in the optional encounter and I'm glad I did, since it led to one of the more tense moments in the scenario. The final encounter had a nice twist to it, so every time the party thought things were completely under control something unexpected happened. The only thing stopping me from giving it five stars was one encounter with slow moving enemies that never got anywhere since most of the party had range.
Preparation was pretty straightforward from a GM perspective, and having the statistics for most of the encounters included in an appendix was extremely helpful to keeping things flowing smoothly.