There are a lot of companies who create firewalls but there is not a single one which can compete with ASA.
It can have access control from layer 3 to layer 7.
The ASA 5510 is more than enough for small to medium business.
It has dedicated GUI interface which is known as ASDM, a beautiful tool to manage ASA.
You can use ASA to route traffic.
AAA service supports plenty of Authentication server types.
You can configure advanced NAT in this device.
It uses Modular Policy Framework (MPF) to inspect traffic.
You can inspect traffic at different layers separately.
You can use this as a transparent firewall & fail over is instant.
The virtualization works beautifully for this device.
VPN is another added advantage.All the types of VPNs are managed through ASA.
Room for Improvement:
The 5505 does not support multiple mode.
While running this device on multiple mode you cannot use dynamic routing protocols or multicast routing.
Also the IPSEC and SSL VPNs are not supported while running in multiple mode.
sometimes analysis might take too long while performing DPI in real-time traffic.
The product is expensive. A 5580 series costs more than $50000.
Its very difficult to write something about this product as it has so many options.
I have studied 1000 pages about this product and most of the organizations use this firewall as it is the best in the world. I have never seen such a powerful device which can handle 2 million connections at 20Gbps speed. It can
also inspect 4 million packets per second.