While a absolute BEAST of a tame, the giga has some factors you have to consider.
1. Enraging. The giga will enrage and attack EVERYTHING if it enraged. Its eyes will turn a luminous yellow colour and it will be angry.
2. Feeding. The giga will enrage (see above) if there is no meat available too it, whether in a trough or in its inventory. This will stop once it has acquired enough meat to keep its hunger away. (This does not apply to babies. They will just starve)
3. Imprinting. If you have a giga, breed it and get 100 percent imprint. If you don't, the giga will enrage permanently until death when its health drops below a certain amount. (I think 40 percent).
4. Using your giga. These things have a nasty bite and would be perfect for pvp except for the fact you have to factor in the above and that you are a sitting duck for any sniper while mounted. Besides that, it is perfect for pvp.
Hope this helps. But remember, these things can still be countered with varying difficulty.