On first impressions they look rather good!
I asked the Perry's about plastic Afghans and they said they had no plans for them, that was a couple of years back. They didn't rule out doing them sometime in the future, but with their Paraguayan War 1864-70 project just announced I'm expecting their focus to be on that for now.
These look like they could be a good alternative, especially if they fit in nicely size wise with the Perry metals.