I have found it to be pretty accurate at forecasting however the caveat is it cannot accurately predict CAT so checking the PIREPS or SIGMETs can help know what is out there.

Also, I have noticed that when it predicts moderate or greater turbulence within the first hour or so it doesnt actually happen. I have put this down to flight planners also knowing this and trying to plan routes to avoid.

But overall its a neat tool and I check it before most flights even though I actually enjoy a decent amount of turbulence.