How is the quality shock you? Is it the size or the number of components used?

probably left hand side looks like a blown transformer...

LHS the rcd (residual current device) shares the same pcb with the water flow switch, and led

RHS has the better design, rcd board is separate, led indicator pcb also separate all ok..

TS make sure you always test your rcd circuit to make sure no risk of electrocution..

if it doesn't trip then send that heater to replace the solid state relay where the Neutral and live wire goes before the heater elements..

test it often..  don't risk your safety..
I don't see a pump motor.. if there is an obvious difference in water pressure might be a stuck or sticking permanent magnet inside the entry pipe

it activates the reed switch which detects water flow which switches on the Solid State Relay to water heater element..

Joven shares similar design arrangements with the RHS heater (but with the snubber rc circuit installed, RHS missing next to push buttons)..

Less components cheaper build but hopefully doesn't actually mean lower quality..

no problem..

RHS there's suppose to be a rubber grommet at your cable entry to prevent insects small lizards from getting inside and shorting out the live conductors.. place it back or just masking tape the opening for prevention..

why not use storage type?

You should see Panasonic quality inside. No brand at its standard.

From the photo, the pensonic look like without a water pump, and circuit are simpler. Like Richard mention, the safety board are independent, which is good.

Both looks poorly constructed
open up a panasonic and you will be more relieved with the protection mechanism.

if you intend to use tank type, make sure make sure make sure you install additional elcb of 10mA non negotiable.