You absolutely need a breaker in the panel, and could choose to make that breaker your single GFCI for the whole system... for me, it was cheaper to buy a spa panel with 50A GFCI breaker, a regular 50A non-GFCI breaker for my panel, and 15 feet of 6/4 wire, than to buy a 30A GFCI breaker for the panel by itself and 15 feet of 10/4 wire. I still don't understand why the pricing works like that, but it ended up giving me future expansion flexibility for my 5500W system.
Primary: Gluten Free Dos-Equis Clone 1.14
Bottle Conditioning: Gingerbread Stout 12.13
Kegged: IPA 11.13
Commercial Tap: Bell's Two Hearted
In Bottles: Hopslam, eSCB Holiday Ale 8.13
On Deck: IPA 3.13
Gallons in 2014: 11