I guess I have/had too almost all the PMs on the market since years (exept SRMs, but I saw files from former clients). There's probably an higher degree of error on a single side PM (and Shimanos) than from these last "Chinese" spiders PM. Not because of hardware (lack of) specs or factory miscalibration but simply because none is pedalling 50/50 (or even 50.5/49.5 thus on/over the +/- 1% accuracy).
In general, with the "democratization" of PMs I saw a lack in general precision on all the spectrum, no matter the price, with the only notable outlier being Favero Assiomas (they learnt a lot from the BePro, remember them?).