Very fun and very clean overall, with great visuals. The core mechanic works really well, and I could easily see this being expanded into a bigger game with different rewards, vault types, power-ups, upgrades, etc. It would also make a great mini-game inside a point-and-click adventure.
My one real issue was the Work Order upgrade page, the text color blends too much into the paper background, so it’s difficult to read.
Otherwise, I had a lot of fun with this. Simple concept, satisfying mechanic, and plenty of room to grow.