We use Optimizely at lastminute.com
Rhys Merritt

Yes, that’s true Rhys Merritt, you can A/B test some minor variations with code blocks let’s say a velocity variable, or score needed to gain stars at each level etc.

However if you want to decide whether your app should require registration or not, you should (in most cases) design and develop two different versions of your app which affects many different parts of your db or user flow. So in those kind of cases, we use staged rollouts.

Hope I explained myself clearly,