Did some performance tests comparing the serialisation speed of Json.NET and NDatabase with my use case, and NDatabase is faster by about 10 - 20 % :-)
I tried to measure the de-serialisation but Json.NET cannot handle immutable types, whereas NDatabase can. (De-serialisation is about twice as fast as serialisation.)
On the home page you should mention the fact that NDatabase can handle Immutable types with private readonly fields as well as classes with circular references. (I have tried a whole bunch of serialisers and there are only a few that can handle these situations.)
Would it be possible to specify a stream instead of a Path to save the database to. This way we could save the database to a memory stream. (i.e. OdbFactory.Open(Stream stream)), and keep everything in memory.