Well, you will find that watts=volts * current, so that is not really an issue. Chargers are supposed to deliver about 5 to 5.2 volts..
You cannot harm a device by using to little current. It is kinder to the battery to charge it slowly.
There are two things to watch for:
1. if the power supply delivers too little current, the chuwi may not charge while running. I notice this with the little 1/2 A charger I often use.
2. Chuwi (or the charging circuit they use) have not implemented the USB protocol properly. The device should not draw more power than the charger offers. The chuwi draws as much power as it can, causes chargers to get hot and can trip the charger's protection circuitry.