Have run this twice now (both low-tier). Here are my thoughts.
Part A: Seems fine, parties enjoyed the antics with goblins, and the combats with the variable secondary monsters were passable if not memorable. The minions are almost too easily taken down, granted it's a moderate encounter. Both parties were looking for clues about why the caravans were being attacked and were sad that there wasn't some indication as to why.
It seems awfully hard to actually destroy a wagon. I focus fired one the second run to see how far down I could burn it. I only got it to halfway. Parties are easily making the DC 14 reflex save, and the PCs seem to know not to let them burn for long. It's unclear if the goblins should die in the initial attack as the wagons burn. It appears they should but isn't called out.
Part B: This portion is meant to provide parties with an opportunity to go off rails and do their own thing, which is good for the replayability. However, there isn't much incentive to do so. And given the nature of the encounter here, it does make the final encounter easier if you play it a certain way, but ultimately could impact player's treasure bundles without them realizing it if they're not careful. Overall, the camp design doesn't quite fit with how many goblins are meant to be there, though goblins probably don't mind squeezing to sleep 4 to a square.
In both games the parties immediately searched for the tracks after reporting in with the job site boss. One group actually decided to not immediately go to part C, but it required me to say that the party had arrived close to dark (something that's not explicit in the scenario as I read it). This prompted them to camp for the night, and setup some defenses. We calculated that most of the goblins can actually fit inside the infirmary, so they boarded up the windows, setup the walls around the infirmary and waited. The climb speed on the monsters proved useful as they were able to circumvent the watch and got to eat some gobbos. Both managed to retreat but were severely wounded. It appears that this is meant to make part C much easier at the expense of potential loot lost. If a party knows how much morale they have they can "spend" some of it to make part C a cakewalk. I expect future runs as players know the scenario to
Part C: As written it can be a very hard fight if parties immediately go, though this varies depending on the primary antagonist. Nothing fancy here, just a straight "boss fight". The primary antagonists who can speak make for interesting villains who can explain their motivations in combat banter. The one who cannot is just a bruiser and the scenario suffers for his lack of background that can be communicated to players.
Keff was hard due to scaling (~90 HP) and the Maul ability. Vanu Mas moderate, with increased mobs, lucky crits can really snowball a party. Overall both parties thought that the combat was balanced, as did I. Be very aware if you run this that in low tier there should not be any repeat monsters from part A. The layout of the statblocks make it appear that they are distinct from the tiers, but they very much are not. Simply placing (Tier 3-4) next to "Secondary antagonists" could've saved this GM some headaches. The overall layout design does little to distinguish the tiers and variants. Indentations or other visual guides would've been useful.