Technically beyond the basic model with pump DH-3RP1MK, you're paying for the push button feature and mounting pole (height adjustable) for the holder DH-3MP1MW, other higher series just nicer plastic casing and chrome bits for the shower head & mount (purely cosmetics)

Cheapest one that fits the bill is the basic model DH-3RP1MK
With Ag+ shower head and pole mounting and push button DH-3MP1MW - I recommend this one coz of the shower head

Recently, I have purchased a Panasonic water heater.

To my surprise, the unit started to leak water from the heater tank 1 day after installation.
This tripped the circuit breaker.
Luckily, no one was hurt.
Now, I'm waiting Panasonic to give a solution.

Lesson learnt, branded heater will also have lemon unit.

FYI, I have been buying Panasonic water heaters only for the last 10 years (about 6 units) and all are working fine until today.
This lemon unit taints the perfect reputation...

i'm looking for water heater with very low noise for pump, is there any good brand/model for this? i can't find much reviews for water heater,