Hello Sergey,
The ASA is not flexible????
What... It's way too flexible,
If you want to assign the same nameif value to more than one interface (you will need to use something like redundant interfaces or a port-channel) but is not what you are looking for,
The ASA is a security device and will let you to create policies based on any of your requirements, there is no such zone concept because we have the ability to create our own polices without the restriction of MUST have a zone-pair.
We have the security level purpose for that ( a dynamic way to make everything easier.)
But I do agree with you.. The router is way more flexible (as a firewall and routing device),
The only thing I see the ASA being better is in troubleshoting purposes
Let me know what you think and also remember to rate all of the helpful posts, that motivate us to keep responding
Julio Carvajal
Senior Network Security and Core Specialist
CCIE #42930, 2xCCNP, JNCIP-SEC