Minor - P4 Rubocop recently introduced a new cop that converts User.count > 0 into User.any?, but Mongoid does not support these methods at the top level. I propose delegating these methods to scoped, which does support them.
User.any? => User.scoped.any? User.one? => User.scoped.one? User.many? => User.scoped.many?
Additionally, these methods pull all records, then perform ruby's enumerable methods on the resulting array, which is not performant. I'd also propose making them use mongodb count function if the records have no already been loaded into memory.