This feels like it is missing something. The end seems rather anticlimactic. After all the searching the PCs discover that nothing is really wrong and they can go home. Making reconciliation with their respective parents part of the adventure would help, but then it wouldn't fit in with the 5 room dungeon.
Perhaps trying to force this into the 5 room dungeon mold is the problem. The 5 room dungeon is set up in such a way to include puzzles, fights, and role-playing, the various styles of play that different players gavitate towards, while this adventure is much more about heavy role-playing with a little puzzle-solving and no need for combat.
If I were to run this, I would drop the 5 room dungeon template and expand it. It doesn't need combat or a climactic scene. It needs resolution. (Also, players who will enjoy it for what it is, rather than looking for things to fight, because otherwise the real gems in this will be lost in the bloodshed.)
I would love to give this a 5/5 because I really like the core idea, the descriptions, and the characters. The servitor imps are a nice touch, as is the locked door that they must talk their way through. Having the other party there to "rescue" the boy could be a fun scene to run if done correctly. I think there's a lot of potential for indepth role-playing here.
I can picture a few dastardly uses for this armor.
Desperate warriors needing to hold a pass long enough for reinforcements to arrive. How to decide who will wear the armor?
The villain pays off a few unwitting villagers to hold off the PCs for a time, neglecting to describe the full purpose of the armor being "gifted" to them.
I love subs that get my mind working on all the possible applications.
I'm always impressed by those who can be so efficient in their use of words. This is something I try for but tend to fall short of. I may just add my own attempts to this list. My all-time favorite is Hemingway's six-word short story ("For sale: baby shoes, never worn.")