I suppose its okay, but it lacks some of the nuance of the original Advance Hammer Jump of needing to stop before it gets used, or like Adventure (which I assume inspired its Advance counterpart) where you need a running start. As it stands now, you're going to be using this jump far more than your normal jump due to being so much higher, effectively replacing Jump with Custom 1 when you load it. There's only a few instances where you would Jump instead of C1, like during a boss fight.
There's also virtually no wind up animation for her hammer swing. I actually couldn't see a single frame during this mode where the hammer is actually out. I can't remember off the top of my head if its like that in advance, but it does bother me a bit that this hammering move has little visible hammering (despite the hammer hitbox). If you had this loaded onto a server and didn't pay attention tot he filenames downloaded, you would be very confused at the moonjumping Amys going around.
Overall, the move is okay, but a few things with it bothered me.
You can actually see the hammer frame before she goes into her "spinning state" while rising. Granted it only appears for a very small amount of frames. I feel like the ideal way to go about this would be to make sprites for her performing the hammer jump. You can kind of see her in her hammer frame while she's rising off of the ground and I didn't really want too much of that to be seen.
At least thats what I think. But yeah I do agree overall that most of the time using this move is better than using your standard jump, I feel like it has a lot to do with SRB2 being a 3D game and it's level design too though. There could also be other things about Sonic Advance's physics that I don't take into account of.
I could have made code to reduce the player's current momentum or speed when doing the move, but it just doesn't seem that hard to pull off a Perfect Hammer jump in advance and wouldnt want to make a move that would be inaccurate to the source material
I WILL SAY however, in some of the rom hacks of Sonic 1 and Sonic 2 that they put Amy in, Amy doesn't slow down in her crouch, she stops ***instantly***, therefore a perfect hammer jump is impossible in that case.