Not a scientific study, but someone did replicate the experiment on themselves [0] and found that in their case, any effect from LLM use wasn't detectable in their sample. Notably they almost certainly had more experience with LLMs than most of the METR participants did.

[0] https://mikelovesrobots.substack.com/p/wheres-the-shovelware...

I haven’t heard about any similar studies, no. I’m planning to conduct one at my workplace but we’re still deciding exactly which uses of AI to test.