“All plans include all features.”

We arrived at this after many years building multiple products. In all products we built we have just 3-4 plans. All features are included in all plans (including the trial plan). Only the usage amount differs from plan to plan. This makes it so easy to explain to end customers and leaves your engineering team with valuable time to deal with improving product. Further the number of billing related support requests decrease drastically. Your support staff also need less training.

The advantages are many to keep billing simple. This has been our experience. YMMV.