I have the AEM, installed for 6 months. Pretty good unit to be fair - though I have no comparison. Certainly it reacts fast enough to work out what's going on. Used it to diagnose a lean misfire and faulty resistive track in the throttle body sensor on my (current) GT injection. Things I like about it are the simplicity of install, auto dimming of the LEDs, operating reaction time and price which included the lambda boss. I don't like the bulky ring around the gauge (quite proud when sat next to TIM oil guages and Stack boost gauge) and inability to only have the gauge and probe turn on when the engine is running (i.e 13.5v+ feed). This last one can be easily sorted with a zener circuit or adapted split-charge relay though, plus am not sure which other gauges would support this feature (but some must do).
If I had my time again it would be tough to decide between the AEM and another gauge (e.g. Stack) in the end it would probably come down to how much tuning I personally wanted to do to the car and how picky I was about all the gauges looking the same.
