Today, I informally tested sharpness of this lens associated to a 13mm extension ring and to a SMC Pentax-F 1.7x AF Adapter, versus a Mitakon 85mm 1-5x Super Macro.
You can click the pictures to see larger version.
Here is the Laowa combo:
My subject is a French stamp (intentionally placed at an angle, in order to avoid front/back-focus problems), here is the stamp in its booklet:
Here is the stamp at 1:1:
Here is the stamp at about 4:1, full picture:
The focus is not exactly on the same place on every photo but it is not relevant as I only want to compare sharpness. Each photo has been taken wide open.
100% extract, Laowa 100mm:
100% extract, Mitakon 85mm:
For information, 100% extract, Oshiro/Bresser 60mm, same combo than the 100mm:
The Laowa looks way better than the two others.