The license model of SQL Admin Tools is a Lifetime License. This model means you purchase the product once in your life time, or your organisation purchased the product once in its lifetime. From that point on every upgrade is free. This model was chosen for a number of reasons, but mostly because it's fair and this is how I would like to purchase all software. I don't want to rent software, or purchase one version only to have it out-dated in a year's time. I want to buy software and receive all revisions without needing to pay for maintenance agreements.
I first saw this license model used by Axialis, a software company that produces amazing Icon and Cursor software.
It seems the most ethical way to charge for software. Some of SQL Admin Tools software contains on open/public domain code, such as SQL Math. Making on-going profit from the work of others seems unfair, so I'm only seeking to profit from the work that I put into these products.
The Lifetime License model thinks outside the box and cuts across many of these standard sales/licensing ideas. It offers a reasonable price one-off purchase, and supplied updates but at no charge. This makes it the most customer centric model.