CO2 is plant food. That's the silliest thing to go after them for. While plastics and metals are fine if you recycle, I also don't really have a problem with their materials selection. I will even give them props for being unique and interesting.
If you want to criticize them, why not start with being outrageously expensive? Or how realistically it's hardly better for the environment than using a battery powered device and rechargeable batteries (I prefer Eneloops myself)?
Holy miss information batman.
CO2 is plant food.
CO2 is used by plants only during the night, the rest of the time it's Oxygen, like the rest of us. Contributing Co2 into the environment, and regular deforestation also go hand and hand. You also assume plants can consume unlimited amounts of CO2, so it's OK to to push it into the atmosphere. There is a limit and it's declining as we increase CO2 output.
Where do rechargeable batteries go when they are done? The landfill. Wax breaks down much easier.
And to begin, the CO2 output from candles is very minimal compared to the CO2 output from the power plants. Also, the candle energy is direct into the speaker, so there's less loss of power while transferring the energy. It's less wasteful.
It may not be practical, but it's a good step in the right direction.