You can also gimp spacies with dancing blade. I've just uploaded an example:
Haven't really seen anyone use it like that - maybe because it's risky, due to putting yourself in danger to get gimped through Falco's own side-b.
I could've also jumped + dair and landed on the stage when Falco used his up-b.
Other than that, side-b to jump + immediate dair, side-b to immediate reverse dolphin slash, and side-b to up-tilt can work on some characters.
While your video still works as a proof of concept, note that no good Falco would ever intentionally side-B in the position the Falco in your video did; if they're jumping and side-Bing that close to the ledge (because they want to grab it as quickly as possible) then they could just fastfall and double jump sweetspot the ledge instead, which is both faster and safer. They also have other options such as jump backwards (out of range of immediate edgeguard attacks) and side-B, or double jump to airdodge onstage.
I think that jab/down tilt/fair, and sometimes dair would be better in almost every situation if not every situation against spacies' side-Bs; they're safer, cover more, and have better followups. Perhaps side-B could be a better alternative than fair if you're already offstage and need to throw out a hitbox quickly, since the float from the side-B could slightly help you to get back onstage to position yourself to continue the edgeguard; though I'm not really sure of any specific situations where it would be significant. Also, maybe it could be used if and the opponent is at high damage and therefore you don't want to risk tippering the fair and not being able to kill off it because they go too high, but this would rarely be relevant since it's difficult/rare to actually get the tipper fair because the non-tipper hitbox takes priority and the opponent is moving very quickly towards you.
Regardless, side-B has extremely little hitstun ad barely sends the opponent away; such that they're is able to airdodge upwards to approximately the height they were at before you hit them if you don't immediately hit them a second time (which isn't always possible). In any other situation, you either want to edgeguard from onstage with down down tilt or jab, or use forward aerial (more active frames, more favourable trajectory, doesn't use up side-B charge).
Covering a spacie's low up-B with side-B is good, though fairly situational. When the opponent is low enough that you wouldn't be able to get back after edgeguarding them with a fair or bair, then side-B will gimp them while allowing you to recover. When the opponent is at low damage and will still be able to up-B again after you hit them with something, using side-B sometimes allows you to position yourself to continue the edgeguard better than an using an aerial. It also has the advantage of not allowing the opponent to walltech because it has such little knockback. It's useful relatively often on Yoshi's Story, because of the close bottom blastline and the walls.
Here's an example from reaper (who uses a lot of aerial side-Bs in general) of using offstage side-B to edgeguard a Falco (both to hit their side-B and then to hit their up-B). The situation is the one I was talking about where side-B could conceivably be able to set up a better edgeguard than fair could have:
There's also backwards side-B while hanging on the ledge, which pops the opponent up and combos into fair or dair. The only Marth I've seen use this is reaper. It seems situationally useful, but in most cases to have better alternatives (dair or bair from the ledge mostly). Since I haven't seen it used much and have only recently started using it myself, what I've written below is pretty speculative (and vague):
It's applicable for hitting an opponent trying to stall near the ledge (such as a Marth using side-B) or jump to it, and also covers jump->airdodge onstage since even if the side-B whiffs because of the airdodge intangibility you can react and cover it accordingly (if they airdodge at a steep angle from below you then you might not be able to hit them back offstage, but you can still hit them). The side-B isn't active for long so you have to predict the opponent's timing quite heavily (the same applies to any other attack from the ledge though; they just cover slightly different things), and it loses to jumping with an attack if you're not intangible.
Doing side-B allows you to fair from the the ledge facing outwards and land onstage (which functions similarly to bair from the ledge to land onstage), or to dair from the ledge facing outwards (slightly different to a backwards-facing dair straight from the ledge). It has the advantage of allowing you cover that space (the ledge and its immediate surroundings) for longer, since you put out a hitbox twice; meaning that if the opponent has the option to drift back to avoid the side-B, then you don't immediately give up the ledge (like you would if you had have done a bair or dair from the ledge to cover that same space). Side-B also reaches further out and higher up than dair, so it can be used to set up dair when the opponent is further away from you (where they would otherwise be out of range).
Here's an example (if you watch the whole set you can see that he tried it about 10 times and this was the only time it worked):
Another example (here he beats the jump->aerial option using his ledge intangibility and then punishes it; he alternatively could've used fair/dair without a side-B here, though from that spacing while a fair would've secured an edgeguard I'm not sure if he could've gotten the tipper dair):
