I have a newly purchased 2013 macbook air. just testing out with an old card, it sleeps with the SD card in. as far as deep sleep I don't know, and I don't know how to check, so that's out of the question. the amount of time it takes to shutdown and restart is like 15 seconds at most, so I just completely shut down when I am done for a while. I don't like using third party apps to control my OS. as far as a lot of the comments about the speed. The SD slot is a great place to put files that you don't really need to access all the time but don't want to permanently delete them and/or want them to be readily accessible still for whatever reason. old notes, presentations, emails, photos, etc. those things add up after a while on a 128gb drive. anything you use all the time should just stay on your SSD. This is just me, but I wouldn't have bought the Air if memory-intensive usage was a daily occurence. Although it is powerful, it isn't a workstation. So unless you're very impatient or find that you move insanely large files around your computer a lot it might be worth it.
I was looking at the nifty because I preferred the style of theirs and I read a bad review about this particular one. But now that i've read this post I think I will give these guys a whirl. it's less expensive than the nifty anyways.
Good post, great comments. thanks.