i pretty much only dair shine bad people, and shields now. Even then not so much any more. dair grab is guaranteed vs no shield. dair grab is a legit mixup vs the people trying to react to/anticipate the shine, as well as a semi-legit mix up to crouch cancel abusers.
generally, the more i dair grab and nair grab in tournaments, the better i do overall. I have a better neutral game than most of Melee's player base, so just taking advantage of falco's grab game, and good stage positioning, I can kind of just take a mid-paced control of the game.
of course, I like to be a flashy ******, so a lot of time time I forget how to play this game and smash my face against the controller in an attempt to look awesome.
also for clarification, shine grab will miss people who like to ASDI down and away, then JC grab, or dsmash (Peach). If you omit the shine, you can beat them. Especially if you have port priority.