I can share a similar approach I'm finding beneficial. I add "Be direct and brutally honest in your feedback. Identify assumptions and cognitive biases to correct for." (I also add a compendium of cognitive biases and examples to the knowledge I give the LLM.

The rudest and most aggressive LLM I've used is Deepseek. Most LLMs have trained-in positivity bias but I can prompt Deepseek to tell me my code is shit very easily.