If you purchase one license, you can install Slide Effect on one computer (well it is a “user” license, so you can install it on your desktop computer and on your laptop, for example).
Once you made a presentation, you can export it as “standalone” and this presentation can be viewed from any computers: you don’t need a license to view a presentation, only to create it.
Situation in my current company is that we got around our instalations around 8 – 10 display screens, and we are willing to have the presentation running in all of them, so therefore i can buy 1 license, work on 1 computer to develope the product and then export the final worksheet to all of them and having them running with one license. Correct me if i am wrong.