Notes about F-smash: Head invincible 2 frames before hit and entire duration of hit to increase priority, during most of the animation, Yoshi is lower than average, so moves OoS are harder to hit with.
The move first hits on frame 12(probably when you'll hit with it), and provides 9 frames of shieldstun (assuming no stale multiplier) so the enemy can't do anything until your 21st frame. The move ends on frame 47, but is IASA frame 44, so they have 23 frames to do something. So for the most part, it could be punished, but they have to expect it and do things very nicely, or have a good OoS option. (Bowser will get you really easy with an UpB OoS, but a Roy might need to WD OoS -> grab to make it worth while (6 frame jump + 10 frame WD lag + 7 frame grab =23 frames, so that might not work.) REally depends on the character and what they can do. However, if players don't know what they can do to it . . . you're probably fine.
Also, if you want to see a slow-mo gif of the move, and Leffen talking about how sweet it is, look in the earlier posts on this thread. . . I don't want to find it atm, but its there.