We use both too. I do weekly config backups of all my devices. I use realtime change detection to keep up to date with any changes being made on the network. And I use NPM for all the daily information and alerts.
The only time they really overlap for me, is when I'm trouble shooting an issue where I can see the problem in NPM and I use NCM to determine any changes made on the device. Otherwise they do 2 separate jobs for me.