Just picked up the IM vs Mandarin set today. I have to say Heart Breaker is awesome looking. The little Mnada-buggy has really grown on me. TBH I think the base design is perfect, it's a very nice military mini-apc type shape, it's the tall turret that ruins it, so I'm gonna fish out an old smaller axle piece to shorten it and lean it back so it looks less obtrusive.
I think the Mark 42 might've been better with gold arms and red hands though, since the majority of his arms are gold and it would help better differentiate him from the other minifigs.