Yes, the king of unusual controls! And it just makes the HLS even more fun to use. I use this as part of a channel strip / console set-up along with the other Kramer plugins. You can read all about how I do that in the manual for my Waves presets here, and you can get the presets here.
With everything at unity, the frequency response creates a nice analog-sounding curve, and the same with the added harmonics.
Keep your input level near, but not too much in the red. This is the way the original hardware was meant to work, and Waves has built the plugin that way. You will find more great hints and settings for this in my Waves presets.