i own stellar phoenix. you can try it free to see if it 'sees' the data but you have to pay for it to recover the files. If you are in chicago at some point or want to ship me the drive with a return box Ill recover it for you.
Is it claiming it's not formatted, or is it just erased? If you didn't delete anything on purpose, or add more data after the deletion, you have a very good chance of recovering it all, unless the flash memory itself has failed, which can and does happen.
There's only so much software can do if the problem is beyond directory errors. If there's a hard failure, you might be SOL. That said, I've recovered quite a few laptop hard drives, which is what the Mac Mini uses, by removing the drive, putting it onto a SATA or IDE PCB from an external FW or USB drive case, and then putting that into a soldering vise so I can adjust the angle of the drive. Failures are often related to motor bearing or head armature sticktion. Sometimes changing the angle of the drive will allow it to work well enough to recover data. Had a whole bunch of IBM/Hitachi drives out of Macbook Pros that did this a few years ago. Must have been a bad run.
As far as software recovery for Mac, there's a great product called CopyCatX that's a fault tolerant copy. By that I mean if you have a drive with hard errors, It won't stop copying and freeze up like a Finder level copy. It will keep trying to copy the bad spot for a bit until it times out. Then it will force the copy to move on to the next spot until it pulls off every possible bit of information. I've had good luck with that on getting back some pretty important stuff for clients. The combination of the that software with the physical removal and messing with drive positions have allowed me to get back data from quite a few drives that the folks at the Apple ''Genius Bar'' would have tossed into the trash without any recovery at all.
Okay, there are at least two types of data loss. Mechanical hard drive failure and ''accidentally deleted'' data. Three in my book if you consider thumb drive electronic failure.
In any case, for the data corruption that is caused either by early mechanical hard drive failure or unexpected system shutdown (inadvertent data corruption), there is GRC Spinrite. And since everyone and their nephew is listing what they have used, whether or not it works, I just wanted to put in a plug for Spinrite.
Steve Gibson is one of those niche-market older curmudgeons who has been writing PC software since day one, and has kept up with certain things very well.
Many tips will help you recover files. Usually, for such purposes, I use Recuva. But sometimes, it cannot restore all the files that I need, so I try to use Disk Drill again. I think this will help you, but it happens that you will not recover all the files with such software. It is better to contact data recovery specialists. By the way, I recently contacted this company on this issue -- salvagedata.com, and I liked how everything was quickly repaired. All the data from my SD Card was restored. Well, I hope I helped you at least in some way...