I guess it depends on how you look at it. From my point of view, having a collection of Danbury mint cars (only a few, the batmobiles and the General Lee) I wanted more metal because of the "feel". If you have a Batpod, I think that the Tumbler looks more metal than the Batpod does. What really makes it look like metal, that gives it the illusion is metal, IMO, is the combination of the rubber tires, and a few small components which are gloss metal. Turn on the lights and for sure you have the metal illusion.
If you stare at the gold rods which hold the fins, then you can see the plastic clearly. Those things are a dead give away to it.
If you look in the interior, again dead give away to plastic.
Overall though, when it is on display, it looks the way the Tumbler should from the movie. The fact it is that matt black really helps it maintain the illusion.
On display, I have to say from people who have seen it, they are completely wowed by it.
When you handle it though, you can definitely tell it is plastic, and with how careful you have to be with it.
Like I said before, I wish it was a diecast metal, but heh, it is not, it looks like it is, and is a great scaled rep of the Tumbler. When you put it on display you quickly get past the way it felt when yoiu handled it.