The MX adapter is indeed of the highest quality. The frequency of issues are significantly greater with the "cheaper" ELM327 devices. The main issue is usually to NOT have the device plugged in while starting up the car. After the car is started, it should be ok to plug in the adapter. OR if the adapter can be fully depowered when the car is shutoff, some of them like the Veepeak have an ON/OFF switch, that is another option. Probably some interaction with the multitude of systems checks the PCM does, and the tool trying to retrieve data likely interferes with that. Not to mention plain ole EMI.
I don't think it harms the OBD port, unless the adapter is really of poor quality to begin with. $5 adapters in $50,000 cars ... no thanks.