Only the coupling capacitors that filter the inputs of the Singxer SA-1 DC are bridged.
This has nothing to do with the DC protection circuit of the device and does not affect it.
The possibility of bridging coupling capacitors existed in amplifiers more than 20 years ago, and is nothing new and a common practice. If DC filtering already exists in the outputs of the device before, the inputs of the next device do not have to be filtered again.
But every user is responsible for ensuring that no DC components are fed into a device.