My Nifty Minidrive arrived today.
I've been using a cut down cheap card like the ones mentioned earlier in this thread, complete with bit of tape to pull it in and out, so I've had the extra storage for a while.
I use a 64GB mini SD to store my itunes music library on a 2010 Air - I used Tunespan to split the library between two locations and it worked well with the cut down card.
So - my Minidrive - arrived today, ordered in the early days of the kickstarted. As reported elsewhere, there's slightly too much glue welding the drive to the packaging, but it's akin to the glue that holds cds to music magazines - with a bit of a wrestle you can get it all off.
Other than that it fits well in the slot - a tiny gap between the green of the drive end and the housing above it but I didn't expect it to fill the SD card slot so tightly it was difficult to remove.
And that's it - it works - my itunes library is as fast to access as before, I can write to the card, and I no longer have an ugly chopped down plastic card sticking out of the slot ever so slightly with a bit of tape on the end.