Perhaps I have misunderstood, but isn't this a pure implementation
change, with no user visible API changes and backward compatible output?
According to the documentation [1], it only supports compression levels 0-3. They're supposed to be comparable in ratio to zlib's levels 0-3. I found benchmarks [2] of an older version that only had compression level 1, which shows its ratio being quite a bit worse than zlib's level 1, but maybe they've improved it.
The library interface seems similar, but it isn't drop-in compatible. It doesn't appear to have equivalents of inflateCopy and deflateCopy, which are exposed by Python's standard binding. There may be other missing features that I didn't notice.
The streams it produces are of course standard-compliant, and decompression works with any
standard-compliant stream, and is probably always faster than zlib.