You should be able to install old "Mumu" and use the old license key. If you want a new version, well, maybe there is something new in it that's really worth 5x

You should be able to install old "Mumu" and use the old license key. If you want a new version, well, maybe there is something new in it that's really worth 5x, we don't know. If the old "Mumu" doesn't work on new machine, and that new machine is listed in its requirements, then it's a breach of the sale agreement from their side. But if it's not, well, sorry, but there's no breach.