I have been researching Meta Knight recently and have a few tips of information.
1: Shuttle Loop 1 and Shuttle Launch 1 have two distinct hit boxes; the sweet spot and the sour spot. I had suspected this up until recently but never confirmed precisely how they worked. Shuttle Launch 1's sweet spot is right in front of Meta Knight as he leaves the ground. Shuttle Loop 1's sweet spot is the visual blade arc that is shown as he ascends, directly in front of Meta Knight, as well as in front and above. There is a star flash that happens when using Shuttle Loop 1. The sweet spot seems to end vertically just before that star flash. Shuttle Launch 1's sweet spot is a lot less defined and is much closer to Meta Knight's launch start position near the ground.
The sweet spot for both has high base knock back, and low knock back growth. To give you an idea of the kind of base knock back it has, if you take Sheik and bring her to Duck Hunt, bring her to the far left of the stage and then roll her to the right once, if you Shuttle Launch to the left and arc it forward so the 2nd hit misses, she will be launched high enough to land on the second tallest branch. If you repeat this at 150%, she will only go marginally higher, enough to reach the tallest branch. Shuttle Loop behaves in a very similar fashion. The base knock back and knock back growth as such that even as high as 200% or more, we will never miss the 2nd hit when sweet spotting as long as we arc correctly.
The sour spot has low base knock back, low knock back growth. However, the knock back growth on this is very important.
Essentially there are two reasons we as players miss our Shuttle Loops. We hit the sweet spot and arc Shuttle Loop incorrectly in tandem with our opponents DI, or we hit the sour spot near the end of the hit box and they are past a certain %.
To illustrate what I mean by the latter, take Sheik to Duck Hunt, put her on the fourth highest branch (left one), and roll Meta Knight towards the ledge. Do a short hop up air and buffer a Shuttle Loop. If done correctly, Meta Knight will be as low as possible to the ground while still doing a Shuttle Loop, not Shuttle Launch. This distance between Meta Knight and Sheik is approximately as far away as the opponent can be before Shuttle Loop 1 will begin missing. Up until 129, Shuttle Loop 2 will connect. After 130, Shuttle Loop 2 misses. Essentially this is the % where a Meta Knight would need to adjust the timing of the move so that he goes for more than just the tip of Shuttle Loop 1 in order to secure a kill.
2: I did not know this previously, but I found out while playing around with the "edge slip" technique shown on the Tourney Locator videos. If you want to grab the ledge as Meta Knight while being on lip of the edge, all you need to do is Shield while holding forward, then let go. Meta Knight will walk off and auto snap. This is how Ito has been doing it in his videos when he ledge trumps while shielding.
3: I found an interesting way to buffer a neutral air off the ledge, but it has to be done from a run. Say you are running right. Run until you are in the running animation. Before you reach the ledge, let go of the stick then hit right again immediately. This will put Meta Knight in to a skid animation. As you skid and are holding forward, spam A. You will fall off the ledge but because it is buffered you will do a neutral air instead of a forward air. This is likely the fastest way of doing this off the ledge, and is ideal if you are in a position far enough away from the ledge to do it.
4: Meta Knight's up air has three hit boxes, none of which send up. The first one is from roughly 0º to 90º of the sword arc in front of Meta Knight. This sends the opponent roughly 50-60º. The second one is past the 90º point of the arc, behind Meta Knight. This sends the opponent about 50-60º behind him. The last hit box is about 20-40º on the down swing of the sword arc, and it sends them at around a 35º degree angle. This is important to note because when you are doing up air strings, you want to be positioned so you are in front of the opponent but not directly below them. If you are directly below them, there is a chance you could hit them on the other side of the apex of the sword and send them in the opposite direction. Also, if they get to the point where they hit the 3rd hit box that sends them at around 35º then you are not going to be able to continue the string regardless of how well you juggle.
tl;dr: just the tip.