Dont get a PLX if you ever want to go AEM. AEM doesnt seem to work at all with the M300, works with marginal resolution using the M/R-500. Innovates arent exactly high on the recommendation list for use with the AEM also.
i personally would have to recommend an FJO with the NTK sensor, NOT A BOSCH. Sure, you pay extra up front for the NTK sensor, but they last like 3x as long as a Bosch unit. so you arent having to replace the sensor as often nor, spending money on it every time. plus, the NTK's are compatible with race gas. I installed the FJO on my friends MKIV, it was very easy. all you need is a positive 12v battery source (not ECU power source) and clean chassis ground, the rest of it connects to itself. then just use one of the Output wires, i think White, for narrow band output to your ECU. then you can use the 52mm AFR guage and mount it where you please. it has the LED style bar around the circumference, but also has a digital readout in the center. it owns faces and i would recommend the FJO+NTK+Guage for ANYONE with potent setups... and hopes of going AEMPro