Using it is good and bad.
If you hit MK properly, he'll most likely not tech it, it's 14% damage (Fresh), and if you stay in the air until the lag on dair goes away, and then fast fall, you may have the opportunity to tech chase. A tech chase leading to possibly an fsmash, hyphen smash (very good damage), dancing blade, or maybe even another grab.
If you do it too slow and MK doesn't do anything in his massive buffer window, MK can land on the ground, which he will do at I believe frame 58, meaning when you dair him he will pop up and most likely have a large amount of time to hurt you.
I guess that isn't too bad, if he lands on the ground you will get the dair, but bleh.