Lenstip claims the Samyang 135mm f/1.8 is the better choice over the Sony GM version

Lenstip reviewed both lenses and came to the following surprising conclusion:

The summary of this test should consist of superlatives only. Let’s face it, Samyang offers you an excellent lens. It’s a device that is able to rival on equal terms with the Sony model and, additionally, in many categories it prevails. Mind you, its price is two times lower than the price of the Sony. You have to admit in such a situation it would be difficult not to recommend the new Samyang.

Samyang 135mm f/1.8 at Bhphoto, Amazon US/EU, Adorama.