Hi Redbeard,
I use Tel Tru guages in my mash tun and my HLT.
Both thermometers have 6" probes.
The length of the one in the HLT wouldn't matter that much but the one in the mash tun, i feel, should get as close to the centre of the mash as possible.
6" probes seem to do the job well.
I see no real need for a thermometer in the kettle if you are using a CFWC but it may be handy if you are using an immersion chiller.
I can't compare the ones from More Beer but be sure that they read in celsius unless you particularly want farenheit and make sure that those units can be calibrated to achieve accuracy.
Another tip that I have found is that if you use one that is fitted inside a tube that protudes into the vessel then ensure that the the last inch or so of the probe is exposed to the medium that temp you wish to measure.
When I first fitted it to my mash tun I had a bright idea to protect the probe when stirring the mash I would leave the threaded tube the same length as the probe.
Well, the result was incorrect temperature readings as the grist inside the tube was not a true indication of the mash temp because after stirring, it became isolated ( not mixed ) with the rest of the mash.
I hope you follow all of this and I hope it helps with your decision,
Cheers
