A couple of thoughts............
Make sure that the balance of the lid is such that when it is leaned on the side of the mizusashi in use it will CLEARLY remain in place easily without "fussing". It shouldn't want to slip, fall over backwards toward the knob, or tend to roll away due to off center weight distribution.
Make sure the top opening will easily accomodate a "standard" chashaku (ladle) at the typical angle that it will hit the form when it is filled with the appropriate level of water.
Make sure it does not LEAK! (Hagi type glazes on non vitrified bodies can be problematic.)
Depending on the type of Chakai........ it needs to be GRACEFULLY carried into the tearoom full of water and set down.......... watch total weight and the way the top might encourage of inhibit slohing and spilling.
Toshio Ohi San of Japan measured one of my mizusashi opening with his fist.