I see there's also a Facebook group for these heaters. It appears to be pretty active as there have been over 1300 posts in the last 30 days as I write this.
Chinese Diesel vehicle air heaters - Troubleshooting & Parts Sales
The About this Group section includes this description (plus other info):
"A group setup mainly to discuss the technical side of these air (and air + water) heaters. That includes the installation, running and repairing of the cheap diesel 'parking' heaters that people have already purchased. The heaters in question are the unbranded ones currently all over ebay, amazon and all the other 'import' websites.
Buying these Chinese heaters is considered a risk by most, so this groups aim is to have a central place to post your findings of the actual heater hardware, both good and bad, as well as help from other knowledgeable heater owners."
(Note- This is a private Facebook group so you would need a Facebook user-ID and approval of the mods to see the posts.)