It’s a survey designed to determine how well your product is resonating with early users, and assess product/market fit qualitatively. Find it here: https://survey.io/
A sample of 40-50 current users should be enough for conclusive results, but the more users you can get to participate the better.
The core product/market fit question is:
How would you feel if you could no longer use [product name]?
And the possible answers are:
1. Very disappointed
2. Somewhat disappointed
3. Not disappointed (it isn’t really that useful)
4. N/A – I no longer use [product]
Plus and open-ended response that would help you understand why.