I like a proper tower PC :)

Besides, small ones don't have room for my five hard drives (not counting the SSD)...

Proper full ATX? Or Mid ATX

Oh. I meant the MB.

Does the M.2 drive have any benefit over a normal SSD? Apart from less space as it's directly on the motherboard?

Supposedly faster on PCI-X lane than over SATA.

Standard ATX, same as the standard one in the picture in here: https://en.wikipedia.org/wiki/ATX

Chrisss: Potentially, yes. Assuming it's a PCIe/NVMe capable slot, you can get much faster transfer rates, lower seek times etc. SATA is limited to 6Gb/s (600MB/s in other words).

Note that M2 is just a form factor and can run in legacy SATA mode, however it can also support PCIe/NVMe mode which allows for transfer rates of many GB/s. The Samsung 960 Evo drive in my machine for example is specced for up to 3.2GB/s read transfer rate and 1.9GB/s write.

I doubt I get that kind of performance out of it, but the point is that for modern SSDs, SATA is the bottleneck and NVMe/M.2 removes that bottleneck.

Edit: Just ran the Samsung Magician benchmark on my drive. Scores are 2,598 MB/s read and 1,758MB/s write. Certainly a lot more than SATA can deliver...