I have not tried the plastic Maynard cartridges. When I shot an original Maynard I used turned brass cartridges.
I have used the white plastic Smith cartridges for years in excess of 15,000 live rounds. I found that the cheaper versions without the metal grommets in the "touch-hole' burned through and enlarged over years of use while the grommet ones resisted enlarging very well.
In gleichem Schritt und Tritt, Curt Schmidt
Not a real Civil War reenactor, I only portray one on boards and fora.
I do not portray a Civil War soldier, I merely interpret one.