Conclusion
At the price Drobo is asking, the 5C is a versatile and well performing DAS with five drive bays. The hardware used is a good compromise when it comes to a reasonable combination of performance and price. Thanks to BeyondRAID and a software for PC and Mac, this is simply the most user-friendly DAS we've had for testing so far.
If you're looking for an efficient and quick DAS, then the Drobo 5C is simply the DAS, which was the easiest to configure. The BeyondRAID feature is just great, but we still recommend using drives with similar capacities. Like with a conventional RAID array quite some space can be wasted if the capacity differences are large.
The Drobo 5C is listed on Geizhals for about 379 Euro.