At that price I think it has a swing 12v compressor. The Engel does also:
http://www.cooler-store.com/engel_12_volt_cooler_16qt_2103_prd1.htm
If the Engel can be found at a similiar price I would go the name brand for parts. But note that most Engels have the hardware on the side, the "no name" has it on the bottom. Neither is better bot one shap/venting may be preferable.
The units closer to $1000 usually have a Danfoss compressor. I don't know the efficiency comparison between swing and danfoss. Danfoss is German top-of-the line.
Edit: I'll add the the difference between a freezer and a refrigerator is insulation. A freezer capable unit gives up a lot of internal space for foam walls and bottom. The parts are the same.
Edit Again: ARB freezers are either made by Waeco or are a knock-off. Waeco is owned by dometic and seems to be the largest manufacturer of 12/24v freezers and frigs. ARB makes metal things for 4x4. It's very unlikely they make freezers. Nothing wrong with that. But nothing special either. If ARB uses danfoss compressors, I suggest choosing based on price.