When Torque sees this he'll be able to let you know the real deal.
In my understanding, the MOTEC systems are stand-alone and are very, very advantageous to fine tuning everything. They are very precise and effective, but are costly and to propely reap the benefits, the person doing the tuning has to be good.
The piggy-back ECU's are much more commonplace; they simply add onto the existing factory ECU and use some of the factory settings as a baseline. Less expensive.
From my experience (which is kind of a lot after I've built a standlone for my Vette), standalones are good for when you have a seriously modified motor, and/or you primarily race and don't really need to worry about a 'street car'.
Pros of a standalone are FULL control over everything
The con is that to get it as good as a factory tune, takes a LOT of work. I'm talking coast down, cold-start, part-throttle in varying conditions, etc. It's easy to toss it on a dyno and tune the A/F for WOT, but as they say, the devil is in the details.
The other con of a standalone is they rarely have as much basic functionality as the stock unit. What I mean is that an AEM or Motec most likely isn't going to throw a MIL light when your gas cap is loose. Forget about OBDII.
When you think about it - why do most people get a computer? Because they want to play with their engine tuning settings. What do they want to play with? Fuel delivery and spark - that's about it. Using a standalone for those adjustments is sort of like breaking out the sledgehammer to put in a finish nail.