They’re more of a hybrid technology. They have some great applications.

Like temporary storage when using regen from a car. They can buffer the energy and help with a rapid acceleration.

Dash cam in a car. They can charge the cap and in the event in a malfunction / event. The camera can continue to record.

Solar lamps. Charge during the day. Release energy during the night.

They’re poor at long term storage. Great at fast and temp storage.