Have they fixed the quality issues with this? I backed the original run of these on KickStarter, and while they were neat, two of the three I received lasted less than a week. We were sent the newer versions, but they frequently had to be removed and inserted to get OSX to see them.

Yep. I was a backer too and received some early, crappy units. The latest revision is really good :)

Needing a tool to remove it is a major flaw. An SD card that only protrudes by a few mm would be far more useful because you could remove it with your finger nail.

Can anybody comment on the speed compared to the internal SSD HD of a Macbook Air ?

Much slower. The flash chips in a microSD card can only do a few tens of MB/s.

The are now full size sd cards that claim 250MB/s, but not micro ones.

How is this different from a 64GB SD card?

This adapter does not stick out ~11mm