hi,
sorry for the delayed response; it`s a long story...
brianG, the eagletree uses a hall sensor [not a shunt].
http://www.eagletreesystems.com/MicroPower/details.htm [4th line]
the max sampling rate on my v2 was 10hz, and i think it`s the same for the v3 [read the page of the link above].
i don`t think a hall sensor is expensive or physically large either... maybe a hall-sensor-equipped esc will probably need a stronger processor if a serious sampling rate is to be fully implemented along with the mathematics involved to close the feedback circuit fast enough [output current adjusting pwm correlative to throttle input; while at the same time looking for rotor position and all other stuff for proper commutation].
don`t know... maybe some will say it`s useless, but imo, a real current limiter [current controlling closed branch actually] can really help in a LOT of things [from reliability to traction control and efficiency tuning]...
on the other hand, brushless tech in rc is still a baby the way i see it... taking a look on what was happening 2 or 3 years ago and contrasting it to what happens now, makes me believe that...