For the price this is a really good bargain.
It's not the most refined product usability-wise, but it just works. It heats up in a couple of minutes, and keeps our VW T4 camper van warm on setting 1 or 2 (out of 6) even when it's -1° celsius outside.
Air bubbles form naturally in the fuel intake pipe between use, because the fuel partially drains back into the fuel tank. But It doesen't cause any problems for the heater, even when there are air bubble in the fuel intake pipe. The air bubbles get sucked away after a few minutes. No issue there.
Build quality seems fine, and is great for the price.
The controls are confusing and not intuitive. The manual is written in poor english and is also confusing. But it is possible to learn to use it.
The control display doesen't turn off by itself when not in use - meaning it uses a little bit of power even when the heater is off. You have to unplug the display entirely to turn it off, which is inconvenient.