I was drawn to a particular quote in his article about the relative security of ISA Server to other popular firewalls in the context of the number of reported security vulnerabilities for each product.
A quick look at www.secunia.com shows that the ISA Firewall (2004 and 2006) have no active security issues. Compare this with any “hardware” firewall and you will see that the ISA Firewall is more secure than just about any hardware firewall.
There are a lot of firewall appliances out there so I didn't do an exhaustive search of their stats on Secunia, but I did take a look at the stats for ISA Server, Cisco Pix, and OpenBSD as those are the three firewalls I am most familiar with in my professional life.
I found those numbers to be pretty interesting. It is not unusual to have a customer request that a two-tiered firewall infrastructure be implemented on their environment. Often this means they request that some type of “appliance”, be that a Cisco Pix or some other third party box painted red and given a secure sounding name, be placed between the internet and the ISA Server that we are implementing for them. Sometimes this is based on the principle of defense in depth, whereas other times it is based on a false belief that a product from Microsoft couldn't possibly be secure. Maybe if they saw the stats above they would think otherwise.