The only thing worth measuring, if you want to know if your product is on the right path, is your product's trust level.
The reason why I like trust and why I think it is worth measuring, is four-fold.
People that trust you, are more forgiving for your mistakes.
Trust correlates to the value of your product. The more value you add, the higher the trust.
Trust inhibits companies from gaming customers. If you break trust, it affects not just your direct customer, but also the people connected to them.
In addition, it is very hard to cheat trust in the long run. Trust is build over time. It isn't a once-off "first impressions" or "last memory" moment. Relationships are kept strong through continuous work.
This begs the question of why you would even want to fake it? If you continously have to work on it, wouldn't it just be easier to just focus on adding value and reap the benefits of trust?
Victor E. Frankl