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1, Whole section, every appearance of exclamation mark (!) usage *after* the option is deprecated and system prints a warning about it. For sake of consistency please change the usage of exclamation mark to be *BEFORE* the option not after.

2, in section 2.6.2.2. Command Options
-C — Checks a particular rule before adding it to the user-specified chain. This command can help you construct complex iptables rules by prompting you for additional parameters and options. 
-> not present in current version

3, in section 2.6.3. Saving IPTables Rules
there is in NOTE mentioned the /sbin/iptables command and /sbin/iptables service.
Shouldn't the service be "/sbin/service iptables" as a service? 

4, in section 2.6.4. IPTables Control Scripts
Firewall Configuration Tool (system-config-securitylevel) - system-config-securitylevel is not present in RHEL6, there is system-config-firewall(-tui)