one of the claims for NM is that it works with the distro config files instead of needing to do it's own thing.
this doesn't match my experiance either.
NM works for most people most of the time, and that's about all that I would expect from any tool like this (there are just _too_ many ways for networking to be configured). my problem with NM is that it has no allowance for the cases where it doesn't work, you have to uninstall it to be able to do anything else.