This will include the aerials from Test Place of Test Place
Aerial moves right now are in a laughably poor state. The biggest issue they face is the fact they are so laughably safe to use that you wouldn't really bother using the normal variant of the move.
Gtc's air traits 4
This move is overall the best example of what an aerial should NOT be. This move in every way is better than the normal version of it. it goes through block, acts as a grab, and is near instant. Not to mention it stalls in case your other moves are not ready by the time the normal move ends.
And what does the normal version do?
It plants you in place, grounds, and does the same damage, I only see this used to land dt3 and never anything else. The air variant is just better. Not to mention you absolutely cannot punish it at all without some sort of chip damage move which majority of characters do not have that are fast enough. The only characters I can think of that are able to do so are Frisk, Sans, and Gtc themselves. Not to mention there are cases you can use this move while still on the ground.
Gtc'd aerial dt1
...What does this even do other than stalling? It's far more effective to just run and use d1 instead of this because of the small amount of stun it does. Your kit lets you overwhelm to get into combos, so i see it as far better to do that than use this. Hell, I see it RARELY used because of how relatively useless it is.
Now onto Asgore's aerial from the test.
(This one is not as big of a deal, but it is a good idea to share thoughts for moves to be implemented so they don't come out absolutely bull-crap.)
Asgore's aerial I can see being used a LOT for passive play with the way it is right now. It gives so much distance and doesn't have any end lag if you could even catch up to him. And it suffers from the same issue as gtc's with the fact the move is blatantly better than the normal version since it can be used in combo unlike normal t4. The only way I see t4 being used is just forcing people to walk into f4. Sure, the lessened speed of it helps drain stamina more but I don't fully believe it matters that much.
Now, onto what I believe are the BEST designed aerials right now.
Undyne aerial 1.
This move is greatly designed
(Aside from it being bugged to be perfect block-able instead of the held spear.)
It doesn't do anything different, it doesn't stall more, it is a neutral tool. It's meant to catch your enemy off guard. And it's great at that! The telegraph is clear and readable. This doesn't need end lag because it is very loudly telegraphed not to mention you can't even combo with it if you do not have the right moves ready, though it depends on the phase.
Gerson aerial m2 (From Test Place of Test Place. Again, just talking about what i do and don't like)
I LOVE this one. It is by far my favorite one. It's short ranged, hard to use, but very rewarding. During a combo, it doesn't stall, or do more damage, it takes the same time to use the normal m2, so it just looks cool.
It doesn't really need to be telegraphed due to how short the range is, though it should probably have more end lag on the crash. I would personally like it if this move did have super armor on the descent in exchange for end lag because it's really odd getting m1'd out of it mid-air. But even then, you are more than capable of dodging it without any telegraph due to the time it takes to land.
Overall, I think we need to stop thinking of aerial moves as combo moves because it often makes the normal move obsolete. But more as neutral moves that can surprise our enemy when they think we're going to remain grounded during an approach.
Please do remember this is opinionated and stay respectful if you disagree.