I used both of these services when they were running, though I only got to use the 158 from Newton-le-Willows on one occasion.
The 158 was a real stagger! As well as being limited to 90mph, you also got to find out where the (quite steep) gradients on the WCML were - electric traction makes mincemeat of these but for a little 158, it's a big challenge! Camden Bank was immense fun!
The Airport- London service was good fun too, although the electric power helped immensly. These trains had an extended pathing break at Tamworth in both directions which in those days turned into a smoking break for the regulars (no smoking on trains at that time but the stations weren't yet no-smoking zones).
I also had the honour of a 309 on one run to London - and it kept time (including the smoking break at Tamworth). Bounced around a bit but it was good fun!
The main attraction for me was the ability to "turn up & go" for a very reasonable fare of (I think) £20 return. Ok it was slow & not always convenient, but it was fun whilst it lasted.