Thanks for the feedback, greatly appreciated.
Card mechanics: You can roll dice twice or draw cards once for same result. :-) Also, the encounter deck introduces uncertainty in its own way: by only drawing 20 cards into the deck at setup means some events simply won't be part of the adventure. GM can also choose to load the deck at setup in different ways (eg draw more spades than hearts, or select specific cards). And cards are just an awesome mechanic that is under utilized (under appreciated?) in RPGs.
Locks: Borrowed from Errant and inspired by Prismatic Wasteland blog post, I specifically wanted to make an adventure that used the locks. This jam was my excuse. :-)
Also, the Cairn approach is to create the world and just put the players in it. Not about "balance" or guaranteeing success. Up to them to be creative and problem solve. Up to GM to make rulings. However, there are avenues to help the players in this adventure: library can answer questions, there's a lock manual the players might find, and the Queen can answer questions too. I had a fourth way the players could use to get help with the locks, but cut it because of space limits.*
Also, it's possible for the same lock type to show up multiple times. PCs can learn from and apply previous experience.
* I cut several things because of space, might release as supplements.