I will add that I don’t mind if, on top o the flat rate, there is a few years of free updates until you have to renew your license, as long as you can keep using your “outdated version“ for as long as you want. I see this model in many professional apps I’ve used over the years (Sketch or Affinity apps for example) and I find it very reasonable because I understand that ongoing development requires investment.
I will add that I don’t mind if, on top o the flat rate, there is a few years of free updates until you have to renew your license, as long as you can keep using your “outdated version“ for as long as you want. I see this model in many professional apps I’ve used over the years (Sketch or Affinity apps for example) and I find it very reasonable because I understand that ongoing development requires investment.