Your question was is the FMU reliable. Yes it is..in terms of mechanical robustness...it probably won't let you down.

In terms of adequacy..that's in the eye of the beholder..it is a very crude way of providing fuel under boost.

Pros:

- always forces more fuel into the engine under boost (if you believe in "rich is safe" philosophy
- reliable (mechanical failure of unit is rare)
- cheap cost of unit
- quick easy install

Cons:

- rich during transition (when manifold pressure goes from vacuum to boost)
- crude fuel calibration (ratio not tuned to individual setup)
- does not give proper fueling during closed loop operation
- overloads the injectors (too much pressure - will cause injectors to wear)
- overloads the fuel pump (too much back pressure - will cause pump wear)

In the end, you are going to need standalone, but if used right the FMU will help you get through until you are ready to buy one..just be careful..