Water heated through immersion rod is not uniformly heated as the heating is done through convection.
Why Electric water heater is better than Immersion Rod?
Immersion rod takes more time to heat a certain volume of water than a storage geyser.
Another drawback is the limited quantity of water availability while you can enjoy continuous water shower using an electric water heater.
Immersion rods are not safe especially for children as it is also quite common to get mild electric shocks from this apparatus, especially from those of poorer quality.
Immersion rod do not have auto off system and hence if left unattended can be hazardous.