From the photos, it looks like it doesn't support standard size 2280 SSDs. Which seems like a pretty big loss to me, I've got a few of those lying around, whereas the smaller form factor SSDs are a bit less widely available (and generally more expensive and/or perform worse).
m.2 is a form factor, not a speed. It could have been the SATA type m.2 instead of the NVMe type m.2 but then it would have needed a SATA controller on the PCIe bus for no benefit. The cost/GB of cheap (SATA or NVMe) drives is about the same regardless if peak read is 500 MB/s or 1500 MB/s anyways.
Okay fair, I just always think of NVMe drives with 5000-7000 MB/s read speed when M.2 gets mentioned and I misremembered that SATA (non M.2) SSDs were cheaper.
Neither of these takes is necessarily incorrect. Officially yes, out of the box it's 1x PCIe 2.0 and you get ~500 MB/s. There is also an boot flag to switch the PCIe from 2 to 3 and it doubles the speed to ~1000 MB/s. That mode is not officially certified as PCIe 3.0 compliant though due to the way its run but it seems to work for just about anything so long as you don't use a really long ribbon cable. https://www.jeffgeerling.com/blog/2023/forcing-pci-express-g...
My concern is that I'd like to be able to swap SSDs with other standard form factor devices (I.e. any recent PC desktop and many laptops) rather then buy something specifically for a raspberry pi.
