Both are extremely simple devices with practically no moving parts. South filter is still less complicated. The plunger in a French press needs to be tight with a rubber seal to prevent grounds from getting mixed up with water directly. The Indian filter need to have no seal except to make sure that water does not leak out.
If a cheap French press is used the rubber seal could lend a taste like burnt Robusta beans: P
Left longer the coffee could end up getting an over exposed soggy taste on the bitter side the Indian filter has no such restriction. The water, by way of gravity, automatically flows, so no question of over exposure. The rate of flow can be adjusted by the force of tamping the grounds.
The machine has to be snugly fit because Indian filter coffee takes time to trickle because of the gravity. The snug fit reduces exposure to air and thus decreases the chance of the coffee going rancid or sour.
The metal filter used in both help retain the flavor and oils.
It is for those who are in a hurry should use the French press those who can take time out for their coffee should prefer a south Indian filter
Lets call the South Indian Filter – “SIF” from now on. It makes it more approachable and simple for typing too :D