I used Windy almost daily for altitude wind, cloud base, & wind gusts. I find the accuracy is very good. I have to cross Turnagain Arm in Alaska 4 times a week. The crossing is less than 5 miles, however, it is the wind from the east that makes it very turbulent. I use windy to forecast the wind and gusts at different altitudes to find the best altitude for crossing, and also, my go/no go decision. In over 300 crossings, I've only had a few times of inaccuracy.
@jessinak I agree! Here in Manila, PH, The ECMWF model is quite accurate in terms of cloud cover, wind (gusts), and rainfall while temperature is more accurate in GFS.