On the whole, I'd rather have loose screws than the one ultra tight one that seems to show up in a lot of the Italian replicas. I know of three companies producing the 1858-63 New Model Army right now. Pedersoli has a very expensive, high quality one made in a German factory. it has won a few of the International Muzzle Loading Committee championships lately. Then there is Uberti and Pietta.
My guess is that you're odds of satisfaction are higher with a uberti though a lot of recent buyers are very happy with their Piettas. The guns are pretty widely distributed and you should be able to get extra parts for either through VTI Gunparts and likely, Taylor & Company. It's nice to be able to get spare parts - especially the three springs for any traditional single action design as even the best ones are prone to metal fatigue and eventual breakage.
At this time, Uberti, Uberti USA,Cimarron Arms and Texas Jacks ( the later two closely associated and dealing in Uberti products actually provide customer service and keep a large stock of spare parts on hand. Pietta offers a list of gunsmiths who have worked on their guns in the past but when I asked for it, there was no response. I also asked them about customer service and got no answer to that either. Likewise, my efforts to warranty register a Pietta LeMat went unacknowleged.
The 1858 remington retained that marking throughout its production. The number refers to the year Remington acquired the patent held by one Beals who developed the design in 1856 immediately upon the expiration of Colt's domestic patent extension. The first Remington .36 and .44 revolvers went into production in 1860 and lacked the hammer rest (safety) notches on the rear of the cylinder between the chambers. Over thenext three years, these were added as well as some modification to the loading lever- base pin assemblys. The final design came in 1863 and was called The New Model Army (Navy). It stayed in production until replaced by a cartridge revolver in 1875. It does appear that the great majority of them were made during the civil war years.