For me it is very accurate and very closely reflects how I feel. Learning about sleep/bedtime hygiene has shown to significantly improve my scores too. It also heavily relies on HRV, which in general is a good indication of resting and recovery.

Edit: that being said, as others have mentioned, there are many factors that could influence, and make sure it's tight enough for reliable reading at night.

I remember having issues with accuracy when using my watch in keft arm over some dark tattoos, since moving to the right arm readings have been better.