Watchguard Firebox firewalls

[<bailey () dcsb net>]

I am looking at the Watchguard Firebox 500.  What I am wondering is, it says that it was Intrusion Prevention built 
into it.  Is this a true Intrusion Prevention System?

Also, does someone need to have both a Intrusion Prevention System, along with a Intrusion Detection System?

Thanks

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