Lewis-H wrote: ↑Mon Nov 18, 2019 10:45 am
If you attach an external M2 SSD to your Raspberry Pi 4 B, you will get significantly faster app opens and file transfers.
Compared to what? SD card, sure, but compared to any USB 3.0 SSD, nope, it won't make any difference.
2.5" SATA, mSATA, M.2 SATA, AHCI, NVMe will all perform the same in a USB 3.0 enclosure. They all exceed the bandwidth the Pi4 is capable of, so it doesn't matter what the internal SSD form-factor or interface is. An expensive NVMe SSD in an expensive USB 3.0 enclosure will not offer a perceivable performance difference over a less expensive 2.5" SATA-III SSD in a less expensive USB 3.0 enclosure.
Lewis-H wrote: ↑Mon Nov 18, 2019 10:45 am
One of the most important improvements in Pi 4 is its USB 3.0 interface. ...the new model has an interface that can theoretically hit 5 Gbps...
Nope, sorry but you are wrong. All 4 USB ports on the Pi4 are connected to a single PCIe lane with 4Gbps bandwidth. So yes, it's USB 3.0, but not full-speed (and shared between the 4 USB ports).
Regardless, even full speed 5Gbps USB 3.0 is slower than a SATA-III SSD (6Gbps), so an NVMe SSD isn't going to go any faster. It will just cost more and run hotter with no perceivable benefit.
You are correct that a USB 3.0 SSD will be faster, but wrong about it needing to be M.2 or NVMe.
NVMe drives are awesome in computers with an NVMe interface (like my Win10 laptop which boots in under 10 seconds),

but they are massively bottlenecked on USB 3.0 and have little to no benefit over a good SATA-III SSD.
My mind is like a browser. 27 tabs are open, 9 aren't responding,
lots of pop-ups...and where is that annoying music coming from?