I think the digital pro kettle's temperature control is relatively
sophisticated. Since heating slows down as it nears the setpoint
(when not in boil-first mode), this suggests the control algorithm
tries to avoid overshoot.
I've used it for gong-fu a couple of times, and the water temperature
has been quite stable. I haven't noticed the instability (overshoot,
I bet) at lower water volumes, since I add a liter of water after
pouring the current infusion's when the kettle starts to get low.
It's within a degree or so of the setpoint by the time I'm ready for
the next infusion. Initially, I measured with my regular thermometer,
too. They only differed when the element has been engaged recently --
the difference is probably just due to transient temperature gradients
and the different sensor positions. (The tea was really good, too --
Harney & Sons' da hong pao.)
Another approach that might be feasible for you is to get a decent
(i.e., not the T-fal Vitesse) non-smart adjustable electric kettle to
see if you like them at all, and if you find you need it, adding
smarts later on as budgeting permits. E.g., I would love to have an
Auber Instruments' plug-and-play temperature controller (or two; or
ten) someday:
http://auberins.com/index.php?main_page=index&cPath=8
HTH, and best luck finding a kettle that meets your needs,
N.
