I can't think of any serious downside to this approach. Maybe if Backbone decided against using `extend()` in future, we would be forced to grow our own `extend()`, but I don't think that is likely.

Backbone.Model uses the `extend()` method internal to Backbone. Taking a look at [this part of the source](https://github.com/documentcloud/backbone/blob/master/backbone.js#L1537-L1557) might make things clearer.