Glad to help:
1) “is it necessary to use other security plugins in parallel with BBQ?”
No plugin can provide 100% security. And each site has its own unique security needs. If you want to protect against bad requests and other threats, then a firewall such as BBQ will help. Then if you want to add other types of security features, like virus detection or whatever, there are plugins that can do it. There also are plugins that do multiple things, like provide a firewall and virus protection. Some people prefer to add task-specific plugins to keep things light and flexible. Other folks prefer the “all-in-one” type plugins that try to do everything. Ultimately it’s your call.
2) “If so, what is it that BBQ is lacking that other solutions provide?”
BBQ provides a super lightweight and fast firewall that protects against a wide range of bad requests. It’s security rules are based on extensive research and designed to give the widest possible protection with minimal false positives. There are other firewalls out there, each brings its own set of rules that blocks different types of threats.
I hope that helps. Let me know if I can provide any further infos.