really low percents are probably the hardest to deal with when the person DIs behind, in which case it wouldn't really be fair to say it's guaranteed but I basically look at it like this:
1. Usually, ppl don't DI the uthrow correctly consistently. Even if the person is insanely good or really knows what to expect, chances are that you have a free turn-around upsmash or whatever you like to hit them with. Pressuring them and/or grab -> throw as fast as possible helps XD.
2. If the person does actually DI the throw correctly, I want to say that it is possible to hit them with some seriously quick timing (I can't say for sure b/c there's been scenarios where someone will be seem like they're DI-ing correctly but I've managed to turn around -> dsmash or walk -> dsmash or maybe get a jab in)
3. Assuming none of what I said works, reading the tech off of the player doesn't seem too bad. They'll probably tech-roll away and you can probably get to where they end up in a wd or 2 and grab them / do some attack as you're wding. If they roll into you then you can probably just do anything as long as you time it right since they'll be right behind you. And if they don't tech you better try to hit them asap with something or maybe jab reset and grab them again.. I def wouldn't jab reset to upsmash tho. In fact, I wouldn't expect to be able to combo anything after a usmash reliably after a bit of percentage, but it has its uses..
btw I think the cg is pretty reliable cept at those really low percents but I'd say maybe after 10 or 15% you should be able to either regrab, turn-around -> dash -> jc grab, wd back and grab w/o turning around, or wd back -> turn-around grab (btw I'm talking about vs fox).
for Luigi until Uthrow -> Ftilt works
0->52