Just a warning about that Seagate drive - it's in RAID 0 and it's not configurable, so if one of the drives fails, your data is gone unless you have a backup.
If you're looking for a portable RAID option, either LaCie Rugged RAID (there seems to be an issue with the TB cable but it also has a USB 3 port, so you have a fallback if the cable fails) and WD My Passport Pro (TB only, like Rugged RAID, cable is integrated to the case, if that fails, you'll have to replace the entire case) are nice options, both of these gives you the option to pick either RAID 0 or 1 (and I think JBOD too).
Edit: I just realized your iMac is 2010 model, so that rules out WD My Passport, since that model doesn't have TB port, 2011 and later models have them iirc.