Quick take
It is worth it when broad dissolved-contaminant reduction is the goal and permanent plumbing is undesirable. It is poor value when chlorine taste is the only issue.
Best reason to buy: no permanent installation
Refillable countertop systems work in apartments, offices and temporary housing without a dedicated drain or faucet.
What you pay for
The premium buys the membrane, pump, electronics, display features and often hot/cold dispensing. Proprietary filters add recurring cost.
When under-sink is better
Homeowners with high daily volume usually get better continuous flow and less counter clutter from an under-sink system.