As Robh says, long term you should do very well (just about anywhere in Brazil should do very well in the long term).
The Zumbi Resorts have good points and down sides - it is up to you to decide which points you are most interested in and therefore if it is what you are looking for.
The good points are that the developments are legally sound, the price is very attractive for Brazil compared to what most agencies in Europe are offering and the development itself is lovely. Lush green grass, directly beach front, clean and tidy and the people who run the development are a lovely bunch. Miguel is a lovely chap and from what I understand he does have some rental plan and agreements going with some operators in Europe.
The down side is the fact that the location is still quite far away from everything (restaurants, hospitals, banks, etc). The access (once you leave the BR101) is around 5 km of dirt track and you drive past some unfinished construction sites to get to the town. But once you are there, the contrast between the development and the cleanliness and the dirt track really makes you feel privileged.
The down sides are reflected in the price and therefore it can be viewed upon as a good investment taking into consideration that the dirt track has been promised to be tarmacced in the future. When, nobody knows...
Hope that helped