One request: please allow the output of either a) a CSV log of every request and it's timing or b) a configurable histogram of request timing, not just some percentiles and averages. That info is pretty much required for doing any more advanced analysis beyond "the service is fast enough". https://github.com/tsenart/vegeta does this really well (but doesn't have the scripting abilities of this tool).
Is JSON useful to you, or do you prefer CSV?
Once I get a chance to test this out, I'll definitely report any issues through GH.
If you should happen to try out k6 in the meantime, most of the JSON contents should be recognizable/understandable just by looking at the output, if you know what metrics k6 collects (which is documented on docs.k6.io). You can try running with e.g. 2 VUs for 2 iterations, to get a tiny amount of output data but something that looks like a real load test: k6 run --vus 2 --iterations 2 --output json=output.json script.js