I use a magnetic, heated stirrer for most things... One thing not mentioned here so far: A one gallon round, glass "thumb" jug. Simply put the chemistry in and bring the water to the proper level and slowly roll back and forth on a counter top. It keeps the materials in sufficient motion without introducing air from over-stirring and/or cavitating mixers. This was a perfect method in my D-76 days to get a gallon mixed. I would then decant to smaller glass bottles for storing and mixing from.

I use a bit of Xtol and use this method to mix 5 liters into a gallon batch. I've got a pre-calculated grid for my different tanks to get the desired ratio from the more concentrated stock. I've not done any formal testing but I'm getting great life from the Xtol (I don't use much as it isn't my main developer). I've used 15 month-old Xtol stock mixed this way on some film that wasn't important and got normal densities but I'm not so confident that I'd assume good chemistry health and use it that old on important film, though!.