I own two of the Euroarms Rogers & Spencer. It's quite a large gun, although appropriate for the caliber I think. The quality is very good. They shoot very nicely and I'm satisfied with them on all counts.
They are different than the Colts; the grip is somewhat more comfortable than my large frame Colts and the Remington, but that's a very personal comment and says nothing about the gun being "better". A Rogers & Spencer is not a Colt nor a Remington, which can be a good thing or a bad thing depending on what you like.
I'm not familiar with Leo Laden's statement, nor do I know what basis the Australian BP shooters used for their evaluation. Was it a comparison of Pietta's Rogers & Spencer vs Pietta's Colts? Or did they compare Euroarms Rogers & Spencer vs Palmetto's Colts?
My personal standard would be whether I could shoot better with a Rogers & Spencer or a particular Colt design, both built to the same standard of quality. I have found that my Euroarms Rogers & Spencers shoot to POA better and more consistently than my Uberti .44 cal Colts, as they tend to be high at 25 yards. At 50 yards the difference is not so noticeable, and I can easily compensate for the Colt's tendency. The Rogers & Spencer's sights are better, although any bp revolver's sights (excepting perhaps the adjustable Ruger Old Army or target model Remingtons) leave much to be desired.
I'd have to say that the Euroarms Rogers & Spencer is slightly better, but certainly not much better, than a similar Colt design by Uberti. My personal choice for enjoyable shooting, however, is a Colt 2nd Dragoon, so I guess being a little better isn't always enough.