The motorsport extender plugs into the eec and you can dial in the WOT a/f and extend the rev limiter. Not sure if it adds any timing or not. I forget exactly what rpm it starts to work either.
A PMS would be a MUCH better choice for all around tuning.
I will say I have seen more than once, stuff posted about it saying they ran much leaner when doing a dyno pull than they had the extender set for and they could not get things fat enough