Updated brake track would be the first thing I would look for. If it does not have the updated brake track I would seriously not buy them. I had to have two older generation wheels warranty replaced because of a wrapped brake track, and since you are buying used (likely won't have the original receipt), ENVE will not replace the wheels should something happen.

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Tough Times Don't Last, Tough People Do.

2.2 already are the new version...(textured track)
The non textured are Enve 1.25

3.4 v1.. smooth track
3.4 v2 .. textured