It is most definitely quicker, yes. And I suppose if NRE is showing the journey details, then it must be valid..? If not then surely you could get out of a PF on appeal!
Just because NRES journey planner shows a journey does not mean it is valid. If you put in from Hull to Howden, it will sometimes tell you to go to Selby and double back as it is quicker than waiting for the next direct train, however, this involves doubling back, and checking all the routeing rules it is clear that this journey is completely illegal on a Hull to Howden journey. If you then click the check tickets and fares option, it will then tell you that more than one ticket is required for the journey.
It is quite stupid, but it doesn't surprise me with the awful NRES site, that the NRES journey planner makes no reference to what is a valid route for a journey at the timetable stage. It will always give you the quickest journey, no matter whether it is valid or not.
Having said that, if you want to go from Stansted Airport to Tottenham Hale, try buying an Audley End to Tottenham Hale ticket. An SDS from Audley End to Tottenham Hale is £13.60 and is valid to travel via Stansted Airport, thus saving £4.10 on the fare from Stansted itself.