Klaus (at Optical Limits) likes it a lot:
Laowa 90mm f/2.8 2x Ultra-Macro APO - Review / Test Report
www.opticallimits.com
I have the RF 100mm version (ie no AF), and I'm very happy with it optically, hand-held or on tripod. It's a little like driving a manual car after years in automatic - when you get used to it, it feels fine.