Reliability, I agree because he's new to Black Powder & has some learning to do, but in the experienced hands it can be just a reliable & weather resistent.
More Powerful? Maybe but only marginal being that these conversion cylinders are only rated at Cowboy Action performance levels not the modern factory defence pressures that is out there, like I stated earlier my little '58 with it's 5.5" barrel loaded with my cast lead 220gr. .456 Lee Conical & a 30gr. load of FFFG Goex is quite potent appoximating what a .45 Schofield will produce in that barrel length "about 700 fps. 240 ft. lbs.."
I will agree that the conversion cylinder would give some advantages of loading readily available .45 Colt cartridges but otherwise that is it's only real advantage.