@PeteRobie No, you don't pay 257 USD every year. This is the price of a single license, including one year of free upgrades. The subscription plan is optional (70 USD by year), and you can renew it at any time, receiving all the accumulated upgrades before to the renewing date, and one year thereafter.
We usually release two major upgrades every year. In the past (the plugin is on the market for more than 11 years), we have released regular upgrades for a price of 150 USD approximately every two years. Now we have moved to a yearly subcription scheme, it let us to release the new features as soon they are developed, and allow to our clients to have predictable costs and guarantees a continuous product support.
Usually with other plugins usually the upgrading policy is not well defined. Sometimes the software is updated frequently, and others much less. But you don't know if you'll have to pay the next months for a new version, or if it will be free. We prefer to provide to our customers certain security about this.