Nospahlot:
I'm very happy about my setup. It allows me to make 24 liter (6.3 gal) batches and I found the pans at a good price.
The immession cooker is in fact a sous vide thing... This is a nordic brand but I found a similar machine in the US:
https://youtu.be/ZZl7EdVoEWIThere are advantages and disadvantages using these pans...
I have a pan inside a double size pan. The result is a lot of water to be heated. The heating element is 1500 watts but when faster temperature changes are needed I have to manually add some boiling water / use an additional heating source.
It's very easy to maintain the correct temperature. The sous vide immersion cooker is set at a temperature 1.5-2 deg C higher than the required milk temperature.
It can't be heated using a normal stove (haven't tried gas).
It's easy to cut and stir because the pan is not that deep. Aotomatic stirring on the other hand would be hard to make compared to a normal vat.
It's easy to drain the pan and you can get lots of accessories (drainpans, lids etc.) And you can even get transparent versions (plastic) if you'd like.
I have tried different vats but they all rust. The real good ones does not but they are expensive compared to these pans.
The oans aren't heavy and they are easy to handle. The smaller pans can fit in my dishwasher if I remove the top drawer and insert a spray nozzle for large items (came with the dishwasher).
The pans stack and does not require much storage space.
Sometimes I wonder if I should start using vats again and my conclusion is that it's just a matter of taste...
You will probably find this link useful:
http://www.perfect-cheese.com/rectangular-pans:-) Danbo