What type of thermocouple probe to use?

I'm trying to find a good thermocouple probe to use to monitor the temperature of the mash as it exits the MLT during recirculation (my Ranco controller with a thermowell
will monitor the in-flowing temperature). My idea is to use a standard T-fitting, and find a male NPT threaded probe that I can just screw in to one end of the T.

Here is a resonably priced example of one that I found:

Thermocouple Pipe Probe

This is a Type K thermocouple, so it just plugs in to a number of standard digital thermometers, like this one: ThermoWorks – MTC Mini Handheld Thermocouple

What I am wondering about is whether I need the "Grounded Thermocouple Junction" or "Ungrounded Thermocouple Junction" version. I don't know what this refers to. I know that I need the "Male Mini Connector" option in order to plug it into my thermometer.

Ok, here is the difference between Grounded and Ungrounded thermocouples, from Omega.com:

Ungrounded:
Grounded:
Exposed:

Sheathed thermocouple probes are available with one of three junction types: grounded, ungrounded or exposed. At the tip of a grounded junction probe, the thermocouple wires are physically attached to the inside of the probe wall. This results in good heat transfer from the outside, through the probe wall to the thermocouple junction. In an ungrounded probe, the thermocouple junction is detached from the probe wall. Response time is slowed down from the grounded style, but the ungrounded offers electrical isolation.

Click to expand...

However, I am still unclear about which one to choose. Why wouldn't I get an ungrounded probe, since they have better response times? What is "electrical isolation" and is this something to be concerned about in the particular application of sensing mash temperature?

Use an electrically isolated thermocouple when there could be a shock hazard or when any voltage present at whatever the thermocouple junction is attached to could interfere with the circuitry that's reading the small thermocouple voltage.

When thinking about shock hazard, also consider failure situations and the environment around the thermocouple. Suppose the thermocouple circuitry grounds the thermocouple wires and you attach the thermocouple to a metal brewing pot. If you are changing a light-bulb and happen to touch 120V at the light socket with that hand and touch the metal container with your other hand, now there's a path for 120V through your body. This sort of thing has happened to people using anti-static mats at electronics assembly stations! However most thermocouple circuitry will be isolated, partially for this reason.

In your situation I'll guess that electrical isolation is not an issue, however I really can't tell from here...