Well Kev the plastic Engel wasn't released until 2008/9, the only reason I didn't buy a metal case Engel was I was waiting for them to release the plastic one and I bought the first one available in my area.
The plastic Engel has same motor/compressor (Fuji swing motor/comp.), my plastic Engel doesn't have the fancy digital LED readout and other goodies the metal case one has.
My plastic Engel has lived in the back of my Disco for 6 years now and hasn't missed a beat, it's been flogged over some rough ground and nothing has cracked or broken, it can run on 240v or 12 without having to buy an adaptor and it has maintained below zero Celsius temps. in Summer when the back of the Disco would have been in the 50 to 70 Celsius.
The plastic Engel when I bought it was $500 cheaper than equivalent size metal case Engel.
I have a mate that works for BFC and the only complaints they have had on the plastic Engel (and they sell thousands) was that it was noisy. I found this to be so when I would pre-cool mine in the house before a trip, I cured this by sitting it on the kitchen table and it was as quite as a mouse compared to the drumming it used to make on the wooden floor. Perfectly quiet in the back of the Disco, if this plastic fantastic had have been a metal case it would look very used by now, still looks good, except for the red dust all through it, Regards Frank.

