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I have one of the OWC ones and my comment would be that Plastic is not a very good conductor of heat. Speed wise, it is fine. (I also own 2 all metal Rosewill ones that NewEgg no longer sells.)
 
I would go with OWC. Had multiple bad experiences when I tried to buy macally once to save a few bucks. The plastic OWC ones have a metal plate on the bottom which dose a good job at taking the heat away from the drive, the clear plastic also makes it easy to stick a label in there saying what the drive is.
 
For only $5 more, you can get OWC's aluminum quad interface enclosure, which has faster Oxford 944SE chipset (vs. Oxford 943 on the plastic version), better heat dissipation, and more stylish design (at least in my opinion).

OWC Mercury Elite Pro mini
 
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