It's an easy pun I know, but the Nifty MiniDrive is pretty nifty, especially if you own a MacBook Air or newer MacBook Pro. Alas, without an adapter it doesn’t work with the 12-inch MacBook as it comes with a solo USB-C port.
All these laptops have limited storage. The Nifty MiniDrive isn't going to drastically increase your storage space. However, it adds an extra 4GB of storage for $39.99 — and every little bit of additional space helps.
The Nifty MiniDrive is a microSD card that sits flush with the side of your MacBook Air or Pro. The good thing about the design is that, unlike spring-loaded SD cards, there's no end section of the adapter protruding. The bad thing is that you have to use the included ejection tool (basically, a hook) to remove the MiniDrive. The tool is small and easily lost. If you do lose it, you can fashion a make-shift replacement out of a paper clip.
The MiniDrive is also Time Machine compatible, but, with only 4GB of storage, that's not really practical. However, if you're on the road, the microSD card is great for making copies of critical files. Even if your Mac laptop gets damaged, those files should be okay, as the Nifty is waterproof and shock-proof. Also, you can swap the card in and out among compatible Mac laptops (alas, this doesn't include the 11-inch MB Airas it has no card slot).
The Nifty MiniDrive is the easiest way to add some extra storage to your laptop, especially without adding any extra bulk. But it's certainly not the most economical. Consider: with it you get 4GB for $39.99; with the My Passport for Mac external drive you can get 500GB for $70 and with the My Passport Pro you can get 2TGB for $299.99.