https://positive-feedback.com/Issue40/clayton_m300.htm
https://positive-feedback.com/Issue42/clayton_m300.htm
http://www.iar-80.com/page6.html
https://forum.audiogon.com/discussions/hegel-h30-stereo-vs-clayton-m300-monoblocks
There is another glowing M300 review out there that was written by Martin DeWulf at Bound for Sound Report, a former Hi Fi Newsletter (that is no longer published) that covered reviews of equipment without taking any advertising money. I don't think you could find the review on-line but the author thought it was one of the best amps he had heard.