I believe their question is asking about the trade-offs of a PureComponent, which is a Class and incurs a performance hit because of that versus a functional component which is always faster than the equivalent component written in a Class-y syntax.
I.e., do the gains from PureComponent exceed the cost of a Class? Personally I would assume they would otherwise no one would ever think of think using one, but it is an interesting question and set of metrics that could be gathered.
