NekTeck Thunderbolt3 SSD Drive
As we slowly transition away from standard 3.5" and 2.5" laptop drive form factors, 'blade' SSD's using small solid-state PCIe flash modules are clearly the future of Apple storage technology. As such, expect many USB-C and Thunderbolt 3 SSD storage peripherals for Mac to be quite small and compact - yet deliver mind blowing data transfer rates running natively on 40Gbps Thunderbolt 3 protocols.
Cable Matters Thunderbolt3 SSD Drive
We currently have 3 widely available and relatively cheap SSD Thunderbolt 3 blade drives on the market which all share the same OEM manufacturer and design, but are simply rebranded with Plugable, CableMatters, and NekTeck logos. All offer Read Speeds exceeding 2200 MB/sec and Write speeds around 1400 MB/sec under typical use. All are currently available just under $400 USD for a 480GB drive.
Plugable Thunderbolt3 SSD Drive
Note: These are Thunderbolt 3 NATIVE drives suitable only for the most recent MacBook Pro and iMac Pro era machines with 40Gbps Type-C Thunderbolt 3 ports. They do not operate in 10Gbps USB-C mode as other Type-C peripherals might on a TBolt3 port. And since the short 7 inch integrated cable isn't removable and there aren't dual pass-through TBolt3 ports - they're only usable directly connected to your Mac or as the last device in a Thunderbolt daisy-chain.
Many USB-C interface drives ship with both Type-A and Type-C cables for use on Apple computers old and new. When connected to a standard Type-A USB 3.0 port they'll operate with a maximum 5Gbps of available bandwidth. Depending on the SSD drive it may still perform identically.
A single SATA SSD is a fine match for USB 3.0 speeds. A dual SATA SSD RAID drive array is a somewhat better match for 10Gbps USB 3.1 Gen 2 bandwidth. It's only when you move into PCIe SSD modules or high-end multi-SSD drive arrays that you're best-off considering 20Gbps Thunderbolt 2 or 40Gbps Thunderbolt 3 storage solutions.
Honestly, unless you're a speed freak or have money to burn, the vast majority of Mac users just want affordable solutions that seem 'fast enough' for their computing needs - and fast and cheap USB 3.1 SSD external drives fit the bill perfectly.
It's Pro users - especially heavy video editing tasks that need and want high-performance, high-end storage solutions. Even then, they lean towards HDD hard drive arrays with huge multi-terabyle storage capacities to meet their needs. SSD-based arrays are only right when there's a massive budget available and storage needs are more modest - such as in music editing studios where file sizes aren't on the order of insane like 4K and 5K Ultra-HD video can be.
These solid-state drives on a card are somewhat like the insides of a conventional 2.5" laptop SSD drive - without the surrounding plastic casing. They also have a pin-edge connector like a tiny PCI card. These readily available off the shelf modules are now being placed in equally tiny drive enclosures for use as backup drives. Several manufacturers have now started shipping mini mSATA USB 3.0 external "pocket" drives.
USB 3.0 Pocket Drive
64-128-256 GB Sizes
You can even build your own mSATA SSD external backup drive with a low-cost USB 3.0 enclosure and pair it with the mSATA solid-state drive module of your choosing from Kingston, Crucial, Samsung, or others. Use Apple's Drive Utility to reformat it for Mac OSX and you've got a great portable Mac SSD drive a fraction of the size of most that's easier to travel with.
MyDigitalSSD mSATA Enclosure
USB 3.0 Case + Cable
Sure, a USB Thumb Drive might be even smaller. But they don't have anywhere near the sophisticated drive controller chips and Read / Write speeds that an mSATA drive has to offer.