Installation complexity!
> The word "building" indicates the level of installation complexity.
> You need to get inside your PC or notebook to install it and may well need a somewhat specialised allen key-type screwdriver to fasten the locking nut that holds the end of the card once it is plugged into its socket.
I'd say it's almost identically complex as installing a 2.5" drive, perhaps even less so. Often you'll have multiple screws, buffers, caddies, proprietary-clip-on-SATA-right-angle-mungers etc.
When working in IT it's easy to forget how difficult things can be for the typical punter but I don't think the installation of an M2 drive deserves the ranking of "complex".
£189 for 512GB NVMe M2 drive... now that is tempting!