The payment model is similar to Spotify and other streaming music services. They take a percentage of all the money from the Unlimited subscriptions and divide it among all the books that were read. But now they are changing it to instead divide among all the pages that were read. The payment per page will be lower than the previous payment per book, but the total amount of money given out will be equal.
Those great books are mostly not being offered through Kindle Unlimited. Most of what you can get is self published works. Some are good, many more are not.
This change is only for Kindle Unlimited and the Kindle Owners Lending Library. You can't download books through those programs (and therefore can't convert them to other formats); you can only read them on a Kindle or with a Kindle app. (There are surely nefarious ways around that, but it's very different from a standard downloaded Kindle book that can be easily converted to another format.) Books that you buy from the Kindle store are not affected; authors still get paid when somebody buys one of those, whether or not it actually gets read.
Amazon probably is tracking what you read on a Kindle or Kindle app in any case. They're just not using the data to determine payments.
Amazon's planned change to payment of authors does not change the payment for books purchased for a Kindle or a Kindle app. It only affects books that you read using a Kindle Unlimited subscription, or though lending privileges granted to you by a Kindle owner through the Kindle Owners Lending Library program. Those programs pay authors using a model that is not unlike streaming music services: they look at all the books read over the month and divide up the revenue from those programs based on that readership.
It's a move on Amazon's part to limit gaming of the Kindle Unlimited program. Authors have been encouraging their friends who subscribe to download their books and open a few pages, which resulted in the author getting revenue as if somebody had read the book. Now they are shifting to actually checking how many pages you read and paying on that basis, so you can't throw money to your friend as easily. It also reins in the practice of carving up a novel into multiple smaller pieces to increase the amount of money received by the author for reading it.
It does have some possibly unintended consequences. First, it means that long books will pay more than short ones, assuming that readers actually read the entire book. (They are using a normalized page count that eliminates variables like typeface and size choices.) It also reduces the amount of money received by authors of things that aren't meant to be read cover to cover, such as reference books.
Java bytecode should always be compatible across platforms, and they have done a good job of keeping that true. There may be rare cases of compatibility issues but I haven't heard of them.
Native code is another matter entirely. That will fail if you move to a different architecture, as could happen if you moved from an old PowerPC Mac to a newer Mac or an x86 system, or when you try to move Java code to a system with an ARM processor. And the libraries have not been as good about maintaining backward compatibility as the JRE has.
Almost anything is more trustworthy than Sourceforge these days.
The direct downloads from the Document Foundation have always been crapware-free; you just have to click past a request for donations to get to them. Windows is the only platform that gets an installer; Mac has a