We A/B test the living daylight out of our application using PyMC3 and custom model diagnosis tools. We also implemented (simple) behavioural models wherever we could. For instance to understand subscription churn, separate measure of retention (probability to come back) and stickiness (how often), and a lot of other fun things!
All our analytics is based on bayesian statistics. It is daunting for most newcomers who have to read a lot when they arrive, but no one has complained so far 