RAID 0 is "striped" which offers better performance but "halves your mean time to failure" as indicated above, since you're relying on two HDDs. Striping does increase capacity as it causes the system to see the two drives as one large drive (no data redundancy).
Striping disks (RAID 0) in general provides a performance improvement. However, for the HR20 and the video streaming operations, there is little need for improvement. The data "flow rate" really isn't going to change since there's pretty much just one application running on the HR20. The only "benefit" is the ability to increase your disk capacity by doubling, tripling, etc. your devices. A larger device should be preferred over two smaller devices in this particular scenario (HR20). You should only need a striped setup if you are using the maximum sized drives available to increase your storage capacity; otherwise, you are increasing your possibility of failure with no real benefit.
RAID 1 is "mirrored" which makes a duplicate copy of your data on the second drive, which offers better protection, since if one drive fails you have an exact copy of everything on the second drive (data redundancy). Mirroring doesn't increase storage capacity, since it sees both drives are seen as one same-sized drive.
The RAID 1 setup, as mentioned here, greatly improves your reliability. If there is some way to know that a drive has gone bad, you can simply replace the bad drive with a good one. No capacity improvement, but significant reliability improvement.
There is also RAID 5 and RAID 4, both of which basically use an extra drive in an array of 3 or more drives to provide both redundancy and improved performance. RAID 10 is a set of striped (RAID 0) drives that is mirrored (RAID 1) with another set of striped drives. RAID 10 gives you both perfomance and capacity improvements as well.
This is just my 2 cents of information.