I've had this for about 6 months now and use it almost daily as a backup for various data files, documents, photos, source code, etc. Build quality is very good. It's quite sturdy although I can't comment on the strength of the keyring because I don't use it. It looks quite nice if that sort of thing matters to you and the little clear plastic switch in the middle that operates the connector retractor lights up when the unit is plugged in. It's quite a bright light too. I was a little apprehensive at first about the way the connector retracts inside the unit rather than having separate cover that snaps over it. I was worried that dust and dirt could get into the unit, but my fears were unfounded.
It's not the fastest USB stick out there though. I also have a Kingston DataTraveler which is significantly faster. I have a batch file I use to back up various data files. The Kingston stick takes just over 4 minutes to back up, whereas this Sandisk takes around 6:30.
When you first plug the unit in to a USB port you're prompted to enter your password to be able to access it. The U3 functions are nice but I really only use the sync program which I find quite useful generally. The sync software stores all data in encrypted form and is password protected. While it's a very useful feature, the software does give the impression of being a bit of a hastily cobbled together afterthought in some ways. The interface feels a little clunky to use and is not without bugs, although I've not found any major "show-stoppers" yet. For example at startup, the software prompts me that a later version is available and asks me if I'd like to download it. I check the "Don't ask me again" box and click the "No" button to skip the download, but it still asks me every time I start the sync program. Just a minor glitch but a slightly annoying one which to me suggests that the software hasn't been tested quite as well as it should be. I would also like better control over which files are backed up. You only get to select directories to back up, not individual files, and within those directories you can select from a choice of 6 different file types or all files in the directory. When you're selecting the directories to back up you can't see the files in the directory either. The most worrying/annoying "feature" though is that when copying the backed up data to another PC it sometimes fails to copy a few files, which
suggests that the copy of the file has become currupted somehow. This only starts to happen after a month or two and resetting the sync'd data fixes it but that means you must then go through the process of selecting all your files to back up once again. These gripes aside, I still find it very useful and it certainly beats manually selecting files every time you want
to backup your data, or writing batch files. You're not forced to use the sync software of course. The unit appears as 2 separate drives (one system/read-only and one data) and you can just drag and drop files onto the data part of the drive as with any other USB stick.
In summary: it's a nice little gadget, well put together, not the fastest available but still faster than most. Sandisk tend to be more expensive than most and so for the money I think you can get better. For my next USB stick I'll probably go back to a Kingston again.