Let me tell my IMHO
-At first: reliability – every English custom gunmaker makes his guns with minimal tolerance (every part perfectly fit to the others) – as a result every part that would move moves smooth and ‘right’ – handling comfort, durability and self-confidence(of the shoter) in every single shot.
Reselling – you can resell the gun for a good price.
And of course prestige (and don’t tell me you don’t care about that, or you haven’t or don’t want to have a Bentley)
About WR boxlock all I can tell – I think it’s a great and reliable rifle but its not a competitor to H&H round because Wr costs 27 000 pounds and H&H 40 000 pounds. But h&H have no any options like royal scroll and regulating at ordered range and others if you include all of this it will cost at least 60 000 puns = WR sidelock
I think it’s a good idea to buy Watson Bros sidelock – 44 000 pounds one of the cheapest at English market