Thanks very much Chris for the help, that’s extremely helpful and as certainly cleared up the uncertainty of travelling along the route in question.
I’d never considered the fare capping benefit on the Overground, and never gave it a thought as I’d always associated it exclusively with the Underground.
I suppose the only downside to the London Overground is the journey times from London Euston to Watford Junctions and vice versa, as there is quite a lot of stations on route (from what I can see on the Citi Mapper app there is 18 stops on route and journey time from Euston to Watford Junction of around 50 minutes).
With regards to using the London Overground service from London Euston to Watford, am I correct in thinking that you will see all the next train times on that route on the screens on the main concourse on Euston station (like I have done with the Avanti West Coast trains), and from there you will see the platform the London Overground train will be leaving on, and you would encounter an Oyster/contactless card reader ticket barrier on route down to that particular platform, and I would see a similar Oyster Card/contactless card reader at Watford Junction?