I'm gathering equipment on the cheap to start all grain brewing and looking at options for an HLT. A rectangular 48 quart cooler is about half the price as the customary 10 gallon Igloo everyone uses on Youtube. Anyone ever used one of these for an HLT? How'd it work out for you?
The shape of the cooler doesn't matter much.
I use a rectangular one for my mash, given the same insulation, they will hold the temperature the same. After 1.5 hour, I lose only 1 or 2°C (and I open the lid to mix the mash at least once).
Round tuns are practical since the lid can be screwed, they are more vertical and may have less dead space in the bottom (depending on how high is the valve location). Other than that, it is not worth paying extra money IMO.