The CS drives are like the WD Reds from what I can gather, a new firmware on a consumer drive.
The feeling I am getting is that they are a step up. The Reds are consumber drives for arrays and the CS are entry level enterprise drives, i.e. they cross the line to the higher tier.
Comparing the Seagate CS 2TB
specs with the WD Red 2TB
specs there are a few differences.
Sustained transfer rate is 180MB/s (CS) vs 145MB/s (Red)
WD do not publish latency so no chance to compare
Power (idle): 3.4W (CS) vs 4.1W (Red).
Seagate don't publish the load power figures.
Warranty: Both have 3 years.
Sample Pricing: US$150 (CS) vs US$112 (Red)
In fact, comparing the specs for the CS and the ES.3 they are pretty close with only the Annualized Failure Rate being a notable exception (1.065% - CS, 0.63% - ES.3).
The ES.2 2TB is around US$185 and the ES.3 2TB is around US$360.
The CS seems like a pretty attractive option.
RB