The api isn't 100% compatible with flumelog-offset? I tried replacing offsetlog in ssb-db/minimal.js to test and I hit:

/home/chrx/dev/bench-ssb/node_modules/flumedb/wrap.js:31
      since.once(function (upto) {
            ^

TypeError: since.once is not a function

When I try running 04-minimal in bench-ssb.