The coherency trick is something not a lot of people think about, so if you can pull it off, it'll make the Gargant well worth his points. It's a bit Gamey, but it'd be hilarious to kill half a squad because you shoved a guy in your pants.
But, your opponent will never let you do it again, and the Gargant is very fragile.
The only other model in the game which can kill specific models I think Is the stardrake. That's it. So, It could be a valuable tool.