On my iPhone, their website does not load with Safari, but does load with a 3rd party browser and I can access the V4.47 firmware no problem. So yeah, try a different browser.
https://www.dropbox.com/s/m57m68efaqpv08n/Topping_UsbAudio_v4.47_setup.zip?dl=0
https://www.dropbox.com/s/m57m68efaqpv08n/Topping_UsbAudio_v4.47_setup.zip?dl=0