Just posted a test of the APO Digitar 5.6/120 lens, at 1x and as a tube lens:
https://www.closeuphotography.com/schneider-apo-digitar-120
I spent a lot time on checking the performance of this lens against the always excellent Schneider Makro Symmar 120mm. Take a look at the results when you have a chance. Thanks. Any questions, send me an email.