I thought my experiences might be of use to some people.
Firstly the Chinese Eberspacher type.
Sold as 8kw. It isn't! No way! 4kw yes.
Pros
Very good value for money.
Clean no fume heat.
Cons
Involved installation
Noisy exhaust - very
Needs a hefty 12v supply as draws about 14 amps starting
Overall rating 7/10