I think it's fine for tools and mods to require subscription to get early access, it motivates modders and tools developers to pour a lot of time not just developing tools and mods but it also update them and provide support and extra customizability with it. However if I am going to be very specific, I think if your tool is made from using data from someone else's research/work, then it feels disingenuous. Obviously FET uses a lot of research and data from FMT and Live Editor and I don't think it's right to be making money from it. If FMT is free, FET should be free too. For original work(fully based on ideas and research made by yourself), it's ok to have early access payment model.