Hi,
This release has a new killer feature - hamsterdb now supports basic schema types for keys. I.e. you can specify that your key is a UINT32 or UINT64, and the btree layout will be optimized for this specific key. The data is more compact, CPU caches are better utilized and I/O is reduced.
2.1.3 is unstable because the file format will change again in the next release, but there are no other known issues/bugs/limitations.