Would you use this for HiFi use - You could. I use it with active monitors, but purely for listening to music, I don't actually do any pro audio stuff. You could use it with as set up that has passive speakers provided you have balanced connections and can fit it either between your DAC and pre-amp, or integrated amp, or between your pre-amp and power amp.
If so, what benefit would this provide over something like capturing data with something HouseCurve/Rew and then using this data via a PEQ setup in your system. - I wouldn't say that there is a completely clear cut benefit. There are pros and cons.
On the pro side, it is a very straight forward, guided process. You can follow the process, take the measurements, set and adjust your target curve, upload it to the "box" and be up and running in 20 minutes or so. Once the measurements are stored in the box, you can pretty much forget about it, as long as it sits somewhere between your source and your speakers, it will be in effect.
On the con side, it only has balanced, inputs and outputs, so won't work with quite a lot of domestic Hi-Fi equipment. Also, you will need an audio interface with a 48v phantom power microphone input to use the MEMs microphone supplied in the bundle, which is an additional item you'll need to purchase if you don't already have one, along with a suitable XLR cable. Although, there is a facility to upload a profile if you already have USB microphone like the UMIK-1.
