Well, my stock shocks on my 2000 Bullet were Armstrongs, and I think that's the standard shocks.
The Hagon shocks are basically updated Girling shocks. Girlings were the sporting shocks in the 1960s. Hagon bought the Girling company, so they are the direct heirs from Girling. Not highly adjustable or anything, like some of the more expensive racing shocks, but very period-correct type sporting shocks.
Armstrongs were the "plodder" shocks for more mundane riding tasks.
That should indicate something about their differences.
I have a set of the chrome-spring Hagons, but I haven't installed them on the bike yet, so I can't actually give any riding impressions about them. But, I've ridden on Girlings before, and they perform quite fine.