It's not just the crack you have to worry about. It's how well it's been cracked. For example, what if the firewall has a crc check inside it, and when it fails the check, it decides to not bother doing any actuall firewalling?

i tried and it worked ;)

Hardware firewalls are not overpriced if you consider how valuable they can be.

You need both to stay safe.
Hardware firewall for packet filtering and software for the application layer.

Just my 2 red.

Regards
SvensK