Just found this thread but as I now live in Redcar I have made good use of TPE’s extended service, though it was meant to go to Saltburn from the start. Unfortunately the much noted troublesome timetable over the Pennines saw the Middlesbrough & Newcastle(?) services swapped in one direction which meant the layover at Middlesbrough became 40 mins not 70, so the furthest they could hit was Redcar and not Saltburn. This has been rectified next December presumably with an additional diagram thrown in (and presumably part funded by our mayor!). It opens up much needed local connectivity but also I suspect TPE may find it opens up Saltburn as a tourist resort to people from Yorkshire and beyond with no/less changes (and cheaper fares). Redcar doesn’t really have this pull, whereas Saltburn will.
I believe there are aspirations to increase the Darlington to Saltburn frequency to every 15, maybe even every 10, minutes in the future - though this obviously requires the huge changes at Darlington to enable this to happen. The Bishop Auckland bit will be the awkward one to solve as it’s almost exactly an hour out & back from Darlington giving zero layover time should it be split and shoved on its own.