Nah I'd never use that , it's powered by the car's USB-C ports so it's just splitting up their power, plus its own overhead (hopefully minor).If that’s no enough charging ports, you can always add one of these to charge an ADDITIONAL 4 devices.
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One can never have too many charging ports.
But yes I do keep an extra USB power supply in the car...a cig lighter one with 45W USB-C + 12W USB-A. Just in case I need more USB power.