Summary: This adapter is really awesome as it has given me the ability to literally breathe new life into my 2 year old 1TB GoFlex drive by bringing it to Thunderbolt speeds. The reason for not making it a 5 star rating is the fact that between the GoFlex and BackupPlus drives from Seagate (both portable and the same form factor) they have changed the shapes so each of these drives need a different adapter which is very unfair.
Summary: I have a ton of GoFlex drives so I bought 2 of these so I can use them on the Thunderbolt port of my iMac. A huge speed jump over the USB 2 port. They come with the cable which is nice. Great value.
Summary: My initial impressions were based on a few HDDs and a (now determined) faulty SSD. I was less than impressed. However, after receiving my new MBA (2013), I transferred my 2 SanDisk 240GB SSDs to enclosures and noted brilliant transfer speeds. It's a little bulky for travel, and really needs a 2nd (pass-though) TB port.
Summary: One problem took several weeks to resolve. The GoFlex switched on the 'Enable disk to go to sleep when not used'. This is found from the Apple icon under Preferences. Seagate sent me 6 emails with different suggestions before resolving the problem. Once fixed the disk worked very well.