for "Mind Games" quest: add BrainHQ suggestion (there is very strong science behind it!+ free exercise available)
1, You already link to the BrainHQ co-founder's TED Talk in one of the quests, called "Your Plastic Brain".
2. BrainHQ has a strong science behind it.
2.1. BrainHQ is the only program that meets all requirements of The Institute of Medicine’s Checklist for Brain Training
2.2. Specific research studies:
and results one might expect: https://www.brainhq.com/world-class-science/published-research
3. They have a FREE-for-all short daily exercise (The Daily Spark) - these are two sessions of one of their paid exercises, every day it's a different exercise.
It, conveniently, takes about 5min (except for Navigation exercise), so it totally meets your criteria for being short & quick.
4. As a long-time user of BrainHQ, I can honestly say that they are NOT your competitors. And in an ideal world you'd partner with each other... (e.g., BrainHQ has big discounts during big holidays and you could notify your users about it...)
For example, I wasn't able to be consistent enough with BrainHQ to see great results because the stuff your tool (SuperBetter) trains (emotional resilience, etc.) wasn't addressed and I couldn't handle the training myself.
to expand on my 4., re. ideal-world partnership: and they (BrainHQ) could recommend SuperBetter for a more wholesome mind training, as a helper in being more consistent with BrainHQ training despite the setbacks in one's life, and as a formal & systemic way to train the good habits/behaviors that they recommend in their monthly newsletter...
(there is no Edit option for a suggestion, so I had to add my update as a comment)