Good so far.
Reasonably good design. Sadly using on a PC w/o Thunderbolt 2 atm, will very likely purchase a mobo with Thunderbolt 2 built in in the very near future, if still available.
Installation was not quite as smooth as I'd have liked, took some restarting and bios tweaking to even get recognized, and then seemed to require a reformat, even though it should have already been formatted. Disc Management in Win 8.1 Pro 64b showed it as unformatted, though Win 8 supposedly can read exFat.
After that, it has been running, and backing up well using the included Genie software. With HDs though, it is a matter of how durable they are, and that can only be know with time.
I also wish the drives were not so proprietary, and hope that I can at some point upgrade their size by switching to a Raid1 setup, switching out 1 drive, letting it repair, and then switching the other, without having to spend twice as much on the specific LaCie replacement drives.