Personally, I am continually intrigued that the initiative passes in HERO and Shadowrun that create a space for speedsters in character design and items.
I've played both a fair bit, and I'd say that cause far, far, far, far more problems than they solve or cool ideas they introduce, on that particular front.
I will literally never play an RPG which takes a similar approach to either, to how they handle speedster types.
In both games, the grand total effect is that speedster gets drastically more spotlight time than any other PC in combat, literally multiple times as many, and in Shadowrun, it also means that they're so much more effective, due to acting multiple times, that if you're not one, but you're supposed to be a non-spellcaster, non-drone pilot (rigger) combat character, you're absolutely terrible and will have very, very little impact on the results of the fight. Especially as not only do you act most, you also likely act first (and definitely ahead of a bunch of anyone without boosts or low boosts).
So basically any failure to take nearly the maximum possible boost that that you can, regardless of anything else, is basically a trap option for those characters (the only thing preventing it being for casters is that casting faster is not always better because of what it costs you). You might live through the combat, but even then, if your "super tough" character gets shot 3x for the 1 shot you get off (and it can be worse than that!), the odds you get messed up a pretty high.
In Champions/HERO (and also the FUZION-based Champions: The New Era), all it does is make the game waaaaaaaaaaaaaaaaaaay more tedious than it needs to be. Those are slightly better-balanced than Shadowrun, because a speedster probably can't afford super-good damage powers or the like (unlike SR, where they can certainly afford a great weapon/ammo), but a good min-maxer can still leverage extra turns to a really annoying degree, and god absolutely forbid you get anyone with the slightest degree of umm and erring, doesn't work out what he's doing before his turn comes, or has analysis paralysis playing speedster (and my experience is, for some hellish reason, those people seem most attracted to the idea! Perhaps because it's the opposite of them?), because they will make the game into an absolutely terminal slog. And again, the spotlight time is very annoying because you get a PC who is literally getting way more turns than everyone else.
(I do know some HERO/Champions GMs did as a result limit how much people could invest into speedster stuff, so that's a possible solution.)
But like, I totally get being intrigued. I was too. It was one of the reason I thought those games were cool. Until I ran them enough.
JMHO and so on.