It's a very straightforward well-engineered piece. The sound is definitely in that API area of things, punchy with a nice sizzle on top. Mixes gain small amount of 3 dimensionality and the transformers impart a nice shimmer.
However, I am selling mine because I've realised going OTB just doesn't suit my work flow, (too much re-patching) so it's not seeing enough action.
I have an otb 16. I like it a lot. Much better than summing itb. Sounds huge and punchy. Calibrating it can be a pain in the rear for stereo channels, but other than that I enjoy having a gain knob, really helps with using outboard.
It's one of the few featured summing devices in our Clipalator, having spent the day with it side by side with other units, I would agree with the descriptions of punch and presence. One of the nicer, more straight-forward summing mixers for sure that definitely brings tone too.
Love it... calibration is a thing, but it's now part of my morning ritual and I don't really think about it... I've been considering a 2 channel attenuator to put after the monitor outs, as I'd like the option to skip the Tonelux transformers and head straight into a vibey eq. Wish there was an option or easy mod for faders for this thing.