Especially considering that with IP24 you're limited to IRIX 6.5.22 and down, and no new security patches are being built for those releases (patches are only verified on current release c, c-1, c-2, c-3).
Another good reason is that you are experienced building firewalls in xBSD. You could have some problems if you're learning on something that security-critical
. Not will, just could, and there's no reason to risk it. Have some fun with the Indy instead.