so far its a really strange assist.
Yes, yes it is. I used to dabble with it quite a bit though and here's some experienced stuff that may help.. Or not.
1. The way the assist works is to center the camera on squigly. It centres the camera both vertically and horizontally, so that means that characters at superjump or double jump height can be obscured by it. Note that it will even take the focus off of a character that is at superjump height... Which is extremely disorientating because of the speed that it happens at and because normally the camera follows whoever is the highest up in the air.
2. At neutral the assist is best used as your opponent wants to run away. It is USELESS if someone is trying to get in against you. Generally speaking, that means its good against peacock, but other than that you have to yomi when your opponent wants to be defensive and run away. If you get it just right though and the assist goes active just as your opponent starts wanting to run away... Its VERY VERY powerful... Like damn near a free opening. All in all though, i think its use at neutral is dubious unless used sparingly.
3. Its best use overall that ive found is midscreen happy birthdays. I dropped the assist originally because i couldnt find any midscreen kill confirms because painwheels combo of slow dash, laggy recovery snap animation and slow normals made it impossible.
4. Its second best use is midscreen corner combos to give you corner only links at midscreen.
5. It is near useless in either corner.
Overall its a very versatile assist that can be used at neutral, in combos, and to allow happy birthdays at midscreen. I dont think its good enough to be a standalone assist on a duo unless its filia or fukua running it. And it has a lot of certain kinds of synergy with certain specials that, while extremely situational, nevertheless can be extremely powerful. Like you can throw lk tears with parasoul and then jump backwards and use sing to make the opponent have to deal with a bunch of about to detonate tears.
Tightest thing ive done with sing, and its real world applications:
At evo '13 during casuals i was playing a against a decent filia that had a habit of mashing air gregor during resets. Well i launched him with pws st.mp and called sing at the same time... (He was in the corner or very near it) he mashed gregor but got sucked toward me by the sing making a corner at my back and i got a full punish. That was pretty tight because that was the version where gregor was still super hard to punish on wiff.
Real world application:
Filia incoming and that gregor mash is expected but dont want to jump and meet her in the air? Call sing and watch her fly into the wall :)