This peice of equipment will be vital to our business operations. ... There are just too many groupscompanies involved in a solution like that (too many opportunities for one group to point a finger at another group). I want a single vendor who can provide support on their equipment with their firmware.
This is no different than many other open source solutions. Just as using a Linux based solution like Untangle will bundle their software on a hardware device, some companies do for pfSense as well. My driving force in the decision is an SLA based on resolution rather than response time. If you call me back to address the problem 2 hours after I report it but then I wait 4 days for the site to be up I am going to have major issues.
The company I use is in Canada but we've managed to get a single source for the hardware, software and support. I understand your need for the one throat to choke, but our switch to open source was based on best posstible support. Switching from buying firewall products to buying firewall solutions made life easier. I know this isn't the right fit for you, but thought I'd add it in case anyone else is reading and considers it.
