With M.2 SSD or just SATA?
Boot Speed never bother my much for work Desktop, as I rarely turned it off, and when it need install update or event just restart, I will take a coffee break. But on my home PC, I usually tuned it off after done, but BIOS seems took a long time. If I am starting build a new PC, might worth consider the difference between M.2 and normal SATA.
As mentioned previously, M.2 is a form factor. You can have M.2 SATA and M.2 PCIe (and M.2 PCIe NVME). I thought I'd mention that again in case you go and buy an M.2 SATA SSD and find out its no faster than a 2.5" SATA SSD.