Merbau is a timber imported from Indonesia. It used to be well priced a few years ago, which is why it was so popular, but the price has doubled in the past few years and that makes it more expensive than the Australian grown hardwoods.
Some of the good features of Merbau is the attractive grain and also the brown/red colouring and the fact that it is a fire rated timber which means it is suitable for use in bush fire zones. A negative feature of Merbau is the fact that it bleeds heavily.
Bearing in mind that all hardwood bleeds to a certain extent, Merbau is by far the worst species for bleeding. If you were to use Merbau over concrete for example, the concrete will turn black due to the bleeding.
Therefore I would not recommend its use for decks that will have a visible concrete, tiled or paved section under the deck. An example of this would be a first-storey deck over a driveway. I also would not recommend its use as a pool deck which has a sandstone, or similar style coping.