I will call sale support to get the long answer..
I will say that if you on the way to buy NPM so you will get more for your money from NCM.
If you are only planning to back up configs up then cat tools may be all you need. The main features added by ncm is the integration into your other Orion products, the config compliance report tool, and the config change templates.
As mesverrum has indicated if you are just doing device backups, then Cattools will do the job.
However, NCM includes so many more features and capabilities to make configuration management, compliance, security assessments so much easier. If you already have Orion NPM, then correlating configuration changes to performance data is such a great thing to have at your fingertips, without having to correlate two different applications and data sources.
Try it and you will see for yourself (I suggest standing up an independent trial instance of Orion NPM and NCM for analysis and not installing against your production Orion)