By the way, I'm thinking of buying the PLM instead of enabling the option on my M800 so I can bring it with me if I choose to switch ECU. (I don't think I can bring the option with me once they are enable to a particular ECU, correct?)
Yes this is correct, the Lambda upgrade will only work on the ECU that it has been purchased for.
Then I stumbled through the LTC and wonder what is the main different between that and the PLM? Beside not having the display and not being able to work with an NTK sensor, will I be able to feed the lambda signal to my M800 to do quick lambda tuning?
Yes, you can connect both the PLM and the LTC to your M800 via a CAN connection and this will allow you to use the Quick Lambda function and record the lambda channel in your data logging.