The swingarm was no easy feat, and reworking the rear susension would have been a chore all of its own, as the linkage will completely alter the suspension spring rate and curve from stock. I'd normally say, I hope the person who designed it knew what they were doing, but from the pics you provided, I'd also say they were probably more than competent. Its a good looking setup, and I'd be interested in seeing more of the detail of it. I'm guessing they did their own version of a Honda Pro Link.
https://gallery.autodesk.com/fusion3.../unit-pro-link