I've got no issues whatsoever. But I did look up what to do before adding my SD card. The general consensus is that:

1. You should update the firmware when you receive it new out of the box, by connecting it as a usb device and dropping the latest firmware .iso into the root directory. I restarted the device after and it started flashing the firmware all by itself. FIIO had been very active on the firmware updates, fixing a lot of things in the process. I remembered the firmware being 1.3(?) on it before I updated it to 2.4 (yes, very active).
2. You need to format the SD card on the actual device before use, and do it twice. I did that with a reboot in between just in case.
3. Always eject the device/SD card properly. The Mini doesn't handle corrupted audio files elegantly and would crash from what I've read. I never had an issue as I do unmount my SD card/Mini before unplugging from my phone. As an additional precaution, I would also turn the Mini off before ejecting the SD card from the device.

Edit: Remeber to refresh the media library every time you add, remove, or change any audio files. The Mini doesn't do it automatically, which does make sense. The CPU is slow enough that the media refresh can potentially be a multi minute affair. I had to wait about 30 seconds for my meager library of around 11GB to load. Not to worry otherwise though, the UI itself is super responsive so far. Just speculation, but I suppose some of the potential crashes may have happened when someone tried playing a missing file.