Actually you only get 25 users for free. After that you have to pay for it. I'm using it on one of my domains and it's very very good, but too low a limit for any decent sized business.
does that apply to nonprofits like k12/edus ?
Can't answer that without making stuff up. :)
Mine's not registered as a company, though, just a personal account and it has the 25 user restriction.