The Nifty Mini Drive is mostly great. You should buy one if you need additional storage for your MacBook.
I ordered a Mini Drive after cutting too much into the hard drive space on my main machine, a 2014 15-inch retina MacBook Pro with a 256Gb SSD, which is of course a proprietary part. I love my rMBP, maybe because it was a gift from my uncle, maybe because it’s an all around champ. However, 256Gb of space just isn’t enough; it left me living like an animal with external hard drives and ugly thumb drives all slowly breaking with every move. My previous machine was a 2011 15-inch MacBook Pro, with a standard hard drive which could easily be upgraded to a vastly superior drive. Additionally, my old MBP was among the dying breed of Macs with an optical drive, which I jettisoned for an OWC Data Doubler, installing a second hard drive and in fact tripling my data. You can get my lightly-used OWC Data Doubler here for free (with free shipping within the United States) if you are the first person to grab the only one available. Occasional random free stuff shall be my reward for enduring my rants, and will hopefully be a new reason for you to read posts.
Enough. On to the Mini Drive; its build quality is excellent and the silver aluminum matches my rMBP perfectly. The fit is also excellent; it sits perfectly flush with the MacBook chassis. Absolutely no part of the Mini Drive sticks out and it simply looks like a part of my machine. The drive came packaged with a paltry 4Gb Micro SD card, but Nifty sells 64Gb and 128Gb Kingston Micro SD Cards for $45 and $100 respectively. I ordered a 64Gb Samsung EVO (up to 48MB/s) Micro SD card from Amazon for use in the Mini Drive. I suggest you do the same. There was no need to purchase anything with a higher transfer rate, since I planned to use my Mini Drive to store mostly word, excel, pdf files and the like. I ended up also storing some audio and the occasional 1080p video which ran without a problem. If you plan on storing 4k video, you may want to purchase Samsung's PRO SD card, which just about doubles the transfer rate of the EVO. For me, the Mini Drive and EVO combination works well and access to anything on the Micro SD Card is fast with no lag or rainbow circle of death. According to Nifty, the Mini Drive will support up to a 128Gb card, so think twice before purchasing a larger capacity card. Nifty includes a rather stylish high gloss metal instrument to remove the Mini Drive, which is nice since it sits completely flush when inserted with no way to easily grab any part of the Mini Drive for removal. Nifty also offers red or silver drive colors and there is no difference in price for either color option.
"Disk Not Ejected Properly"
Perhaps the only annoyance with the Mini Drive is that OS X deems it an improper ejection if you put your MacBook in hibernation mode without first ejecting the drive. In these instances - which may be triggered by simply closing the lid of your MacBook - OS X pops up the same warning as if you had just violently yanked a thumb drive from your Mac without first clicking eject.
Still, its tough to ding Nifty too much for this issue since the blame (if you can call it that) does not lie with Nifty alone. Further, properly ejecting the Mini Drive before closing your MacBook or otherwise triggering hibernation, prevents the issue. Of course, you will likely have to remove and reinsert your drive or restart your machine before the Mini Drive will reappear after it has been ejected. Simply relaunching Finder will not make the drive reappear. Tip: If you like a clean desktop free of clutter, files, folders and drives, pop into Finder Preferences, and uncheck "External Disks" under "Show these items on the desktop".
I strongly recommend Nifty’s Mini Drive to anyone looking for easy expandable storage for their MacBook. However, be sure to pick up a Samsung EVO Micro SD card as a companion, or a PRO depending on your use case. You can snag the EVO 64Gb or 128Gb versions for $18.99 and $39.99 respectively on Amazon. I've been using the Nifty Mini Drive and Samsung EVO Micro SD card combo for about 4 months; it has been convenient consistent performance at a great price.