Someone added a PR with some benchmarks. Here they are on my system doing 1000 set/gets each time in 4 blocks [core i5, 8gb ram, ubuntu 15.04]

    user     system      total        real
    set:      0.150000   0.080000   0.230000 (  1.093421)
    hash set: 0.110000   0.120000   0.230000 (  1.085441)
    get:      0.150000   0.040000   0.190000 (  1.091698)
    hash get: 0.110000   0.060000   0.170000 (  1.075470)

I've done no benchmarking yet. It is a piece that evolved initially from a project I was doing to just explore git's innards a bit more. I eventually gave a talk on what became v0.1 of this (only string store, no typing) at the Columbus Ruby Brigade, and have just been hacking on it a bit in the last couple of weeks because I've found it intriguing.