This can be used as a drop-in replacement. It disk format is compatible with leveldb. But once you upgrade to RocksDB, you won't be able to switch back to Leveldb (unless you restore ur data from a backup).

One definite use-case for RocksDB is a message queue that has a high number of puts/gets/deletes.

Also, please look at options.h to determine what options to tune. A not-tuned system will not show you much perf difference from leveldb.