I was looking at his arm in the video game when he used either his secondary weapon or fusion cannon, but the arm looked like his leader class arm.
I haven't really seen much of the video game, but I'd say the Voyager version actually is the one that comes close to the visual look of his "Murder arm" in the film. I think the leader would have probably looked better, if it somehow actually folded over his forarm, sort of clam shell style, after you fold it down. In fact looking at the design, it almost feels like that was the original plan, but then got scraped for some reason.
In terms of movie accuracy, I hate Leader Megatron's cannon arm. He never had anything so big in the movie. It's huge, immobile, and looks awkward. It's pretty much why I'm not going to spend 45 dollars on him. Just think, if they had made it smaller and more transformable, the cannon on the tank wouldn't be so large, and his tank mode would be much more compact and screen accurate. I did read somewhere that the Leader Class toy was based off earlier designs, with the Voyager being created later after designs were more finalized. But oh well, I'm sticking with the very cool Voyager class for now.
His cannon arm isn't very accurate (I know for safety reasons the blade part wouldn't be very long...but how's he going to impale Prime with that thing?), and it's lack of mobility hurts his posability.
