owned a Drobo S, 5-bay, USB3.0. Have been quite happy with the performance and the strength of its BeyondRAID technology. I know it is extremely expensive but how much value can you put on your data?
I have owned numerous DAS from different brands and find that Drobo works as advertised. I don't mind paying for another unit if I have the need for future expansion and got the budget for it.
Have tested the BeyondRAID by simulating drive failure in ejecting up to 2 HDDs while the drive is powered. All my data recovered successfully although it took more than one day to recover the data from a 2 drive failure. At that point of time, my storage was around 2TB worth of data.
As for speed, it varies as it depends on the type of drive you have installed. If you have the latest and greatest, expect extremely fast speed. If you used last generation of HDD (SATA2), dont expect good performance...
If you have purchased the latest 5D, and installed a mSATA drive to act as a cache, I think the performance will fly through the roof...