It doesn't cover base models that can be upgraded to match the constraints.
E.g.: If I add a constraint "laptops with at least 16 GB of RAM" it doesn't show the Retina MacBook Pro 13". Only the 15" model is shown, because there is a default configuration with said amount of RAM.
Because of this, it is pretty useless unfortunately for those that customize their laptops when buying online. This is most useful for those that just want to go into a store and buy something off the shelf, but then having this online isn't that useful.
E.g.: If I add a constraint "laptops with at least 16 GB of RAM" it doesn't show the Retina MacBook Pro 13". Only the 15" model is shown, because there is a default configuration with said amount of RAM.