I originally happened upon downloading this character from a random netgame, but after trying him out for myself, he INSTANTLY became my favorite character as well as my main. Everything about him just clicks near perfectly, and it culminates in him being one of the most powerful characters created despite his simplicity.
First off: his sheer speed. Robe has the power to absolutely blitz through any level in record times with, get this, minimal skill requirement due to his simplicity. He's essentially the beginner's speedruning character. His Electric Vortex lets you get an INSANE amount of speed near instantly, and Shock Jump allows you to fly over almost any obstacle. Combine the two and it's possible to take shortcuts at lightning fast speed. The only problem with this is bumping into walls, but so long as you stop holding spin, redirect yourself manually, then reactivate Electric Vortex, it's not that hard to get around. To put it in simpler words, Robe is essentially Sonic and Tails mixed into one character - having Sonic's speed to blast through zones and Tails's ability to fly over obstacles or up to elevated paths. And so long as you keep his battery charged, you're set to easily speed through zones. Other characters can still clear zones faster than Robe could ever hope to, but that doesn't discredit Robe from being an easy choice for speedruning a zone (especially if you want a time trial emblem).
Second: Robe makes completion easy. With his ability to magnetize enemies and rings, getting as many rings as possible or getting insanely high scores becomes almost trivial. To prove this, I went and got as many rings as I possibly could in Aerial Garden Zone, the biggest and most stressful stage to get the ring emblem in due to the excessive Hive Elementals and Bumblebores. With Robe, the threat of these enemies became almost nonexistent due to the fact that Robe can just absorb the Bumblebores with his abilities. It took an entire hour, but I was able to greatly surpass my old record and get 1169 total rings!
And third, his only drawback: very specific enemies that are bad for Robe and make levels that have even a single one of them annoying to deal with. Robe relies on sucking enemies into him to kill them, but there is no bias for this, causing him to suction enemies that hurt him before he can hurt them. Explosive Mines can't be destroyed normally, so when Robe sucks one, the mine gets right up in his face an explodes before it's possible for Robe to escape. Spincushions are annoying in that they hurt Robe if they're either currently spinning (making them invincible) or Robe is above them. You need to be extremely careful dealing with these. Pointys are also a threat if you're playing a mod level that uses them. Sucking them either works or hurts Robe, it feels random. But by far Robe's worst nightmare is Green Snappers. There is no safe way to suck these enemies, and in trying to get away from them or even avoid them, you may accidentally suck them, hurting you.