I should say right up front, that I am a KISS brewer and only do single infusion, single batch sparge brews.
That having been said, the canning pots work very well for me. I heat my strike water in the top pot ("mash tun"), dump in the malt, cover it up and wait an hour. It holds the heat well and the temp only drops about 2° over the hour.
As far as temp accuracy is concerned, I can't really say much, as I only turn them "on" or "off". I have played with the dials a bit and they seem to be accurate enough to turn on or off around about a certain temp but being analog, I wouldn't trust them. If you want to do stepped mashes, I would recommend adding something to stir the mash and some sort of external digital thermostat to control temp. A friend of mine has motorized paddle and a BrewBot, which seems to work pretty well for him.
Boiling in the second pot is pretty good too. It heats the wort (~328L) up to a boil in about a half an hour. I have added some insulation around it in an attempt to get a more vigorous boil, but that has been of marginal help.
I have a small refrigerator with what you are planning on doing for fermentation control. I added an analog thermostat with probe for better cooling control and wired it with 2-Way 3-Pole On/On Mini Toggle Switch and aquarium heater so I can switch to "heating mode", when needed.