That link is for an Open License. The MS Open License program allows you to purchase volume licenses individually, but the initial MS Open License order must be for at least 5 licenses (of something).
If you were supporting multiple users in a small business environment definitely make sure you buy as many Windows SKUs as you have end users to be compliant, however.
All of this becomes moot once you have >25 clients; then you can transition to using volume licensing and it's essentially unlimited. It still tracks it though and Microsoft can ask to look at it, especially if you change from Open to Select or some other volume pricing agreement, so keep that in mind.