As someone who has designed some simple products with USB-C, what I can say is that the issue would mostly occur if the device tries to implement a fast charging mode by trying to talk to or sense the cables and power supply. If they follow the USB C spec properly, it will take in a maximum of 5 volts at 1.5 amps when using a "smart" supply (i.e. a Type C laptop/wall wart/portable charger). Or, if it's a simple A to C cable, it will only take the 5V a normal USB Port is supposed to supply.
Then again, I could be oh-so-very wrong. But in my personal experience, it's been fine as long as precautions are taken.
Besides, these devices are usually a bit on the pricier side, I think a few extra cents on the BOM to add an over-voltage protection on the USB Port shouldn't be that hard/expensive.
