Tetraodon mbu is a difficult fish; Stuart Morse wrote an article called "Mbu for You?" where he argues, cogently, that they're simply too big to survive for long in home aquaria. Google the article; it's on various web sites as well as having been printed in TFH magazine some time ago.
Obviously when young it can be kept in any aquarium offering adequate size and filtration rates, but as it matures, you need simply huge aquaria: Stuart recommends around 1000 gallons. While some might argue that's overkill, not many of those who've kept them in smaller tanks have kept them alive long enough for the puffer to reach full size. The main issue is perhaps water quality, in particular oxygenation, so a smaller tank, but one with very strong filtration (super-high turnover rates, say 8-10 times the volume of the tank per hour) might be adequate, especially if steps were taken to keep the nitrate levels low. They are riverine/great lake fish adapted to strong currents and deep waters, and are much more active than many other Tetraodon.
Here in the UK some shops won't stock them, notably the Maidenhead Aquatics chain, simply because virtually no-one outside of a public aquarium can keep them properly. That said, they're fairly mild mannered on the whole, though I agree with Aqualog pufferfish book author Klaus Ebert that this varies, with some being distinctly more "forward" than others.
Cheers, Neale