I've used this service a couple of times since it was rerouted. It's not a very useful service in general as it is quite slow and grinds to a halt near the Greenford East signal Box (seen above) as the signal (a semaphore bracket type) is approach controlled. However in times past the Paddington service departed from Gerrards Cross and picked up at Denham and West Ruislip so it was used by quite a few people, though not many on the return.
No NR ticket existed for the West Ealing to High Wycombe (non stop) return journey at first, though this has now been corrected.
Before Northolt Junction was remodelled the service would pass the up platform at South Ruislip non-stop and take the main line to Paddington (the Marylebone route was indicated with a feather up till the remodel). One day some track workers were on the up line when the Paddington appeared. The lookouts did not need to warn them as they knew where it was heading. The workers however suddenly looked up with alarm and threw themselves off the line, only to see the train go the other way. Whoops, a few red faces.