Whenever I have used the SOU-MAN on Eastern it has been at least 2/3rds full. However, the stop start Eastern schedule is hopeless. It is canned until at least October, but when I asked if they would actually operate it - they said they couldn't guarantee it. So, I've booked via LHR to get to SOU.
From 6 x Dash 8s a day to nothing. You can blame covid etc for the big reduction, but given that the trains are so slow, expensive & frequently on strike there was never a better time to get some reliability into the route & at least provide a day return schedule. Many of my booking on Eastern were cancelled late, so alternative options became expensive, so now, I wouldn't book at all. If only Loganair would take it on, I wouldn't hesitate in booking.