This device lets you control any midi map-able parameter by the velocity of your external midi hardware, meaning you can control audio effects, sample and sound control by hitting or PUSHing quiter or louder on a pad/trigger/e drum or on things like an Ableton Push.
Setting up this device for the first time might be a bit complex, as it needs an internal virtual midi connection on your computer, so if you want to understand and use the full potential of his device.
You can get this device plus a full video course for 20 Euro (plus EU tax) on how to set it up and use plus 2 Ableton Live example sets here: http://abletonkurse.teachable.com/p/velo2midi/