My experience - I installed the MM3 prior to any modification. Drove it that way for a couple weeks, no tune loaded on the truck. I wanted to see what the truck was doing before I went any farther.

I had to agree each time the unit powered on. I was able to monitor the outputs and sensors through each PID that I tried (Nope, I didn't come close to all of them). I left the unlock cable installed, and did occasional remove the MM3 display as I had it on the windshield mount. When removing the display, I would unplug the OBD-II as well, and tuck it under the dash. No issues when I would put in back on. As others have said, watch the plug carefully when installing / re-installing.

The only menu items available were ECM and DTC.

After flashing the ECM, the other items showed under the ECM menu. Including the TPMS. I have not had to agree since then. A side note I have seen asked in other posts, I did have a light on - front O2 sensor, when I loaded the tune. No lights or codes present after, it cleared everything related to the systems it touches. I can't speak for any codes that would be present for other things, but suspect that a code for something that is still active would be thrown after tuning as well.

What you get for choices is dependent on the year of your truck. As an example, my '12 does not have the ability to select and leave on the exhaust brake when restarting the truck. I understand that the 2013 and newer do have this ability (If I am off on the year, someone please correct me). So same MM3, but different options depending on the model year and how the hardware on the truck is integrated.

Hopefully this helps.