So long as you can get f112~slide, 2~MBgrab after the double u3s after either b1u3 or f3, you should be good imo. Very solid damage for a standing vortex and only one bar. You truly only need 3 mixups at MOST if you get that down. I'm a "fun" KF player; I know enough to use her but really just use her because I like the character and don't take her that seriously. You should give her iceberg combos some thought. They really aren't hard at all and can be hit confirmed instead of going for a slide. They build more meter and do more damage too
Do you mean the mb.freeze, j1~mb.freeze reset? Cuz it's totally viable, just takes practice (and offline only). You're spending another meter for a reset that's actually os backdashable (it's possible to time your back dash to block the overhead option and the command throw) - a reset that's also scaled pretty heavily (8-10% less than what her high/low pays off. It's viability is that it's a gimmick that nobody uses, so people haven't practice that os - or likely even know about it. So, in the hypothetical situation that winning/placing a tournament or if money's on the line, then it's worth it. It helps that it's unpunishable since the backdash escape leaves you at positive frames in most situations.
It's best use is in the corner where you can use those plus frames (if they backdash escape) for frame traps/50-50s, depending on the characters backdash recovery. Obviously the Lex backdash punish option makes it godlike in that match-up.
Outside of the corner though, I think it's not worth it tbh.