@mgrouch KMeter is just the thermocouple converter. The TC insulation itself can be made from plastic or silicon or it can be made from glass fabric. It can also be inside a stainless steel housing or whatever. It depends on the application.
I just did a quick search for exhaust thermosensors and there are many K-type thermocouple in different housing available. As long as they have a TC connector or open wires for mounting one by yourself you can use them with KMeter.
I strongly recommend you to read the basics about thermocouples and how they work. You may than understand, that this "plastic thing" can be and should be far away from the high temperature exhaust.
By the way: If you feel better with the MCP9600 then buy one from e.g. Adafruit and use it with its library in the Arduino environment. You controller can still be M5. As for the KMeter the MCP9600 breakout is not made to put in the exhaust as well.
