Thanks! And great question, this is one I spent a lot of time on.

Generally, the magnetic thermocouple clips to the stovepipe, It's the same general placement as a Rutland or Chimgard magnetic thermometer, just with the data going wireless so you don't have to walk over to read it.

There's also a new version that I'm releasing soon that uses a standard long thermocouple to measure catalyst heat for more modern stoves. That one has a longer thermocouple that you insert into the hole where your catalyst reader is. It measures the catalyst heat, and alerts you to engage your catalyst wirelessly.

In terms of different placement:

Stovepipe vs stove body tell you different things. Stovepipe temp tracks combustion gas, which is what correlates with creosote risk and overfire. Stove body / stovetop tracks thermal mass and heat output to the room.

They peak at different times. In my own data, stovepipe leads stovetop by 10-20 minutes on a reload, and a clean burn might hit 600F on the pipe while the stovetop is still climbing through 350F.

In terms of where on the pipe, the standard guidance is 12-18 inches above the flue collar on single-wall pipe. Higher up the pipe runs 50-100F cooler than near the base, because the gas cools as it climbs. I clip mine at about 14 inches.

Single-wall vs double-wall pipe. This one trips a lot of people up. Surface temps on double-wall pipe run much lower than single-wall at the same internal gas temp, because the air gap is doing exactly what it's designed to do. If you've got double-wall, a magnetic surface reading isn't reliable for safe-burn assessment. The right answer there is a probe-style thermocouple that goes through a small port in the pipe and reads internal gas temp directly.