Isn't the another significant different in the logistics of distribution?
For UBI, you need to / get to have a direct line to every person/citizen. For NI, they come to you.
I honestly have no idea which one is better/easier from this perspective, it just seems like the logistics implementation is another significant difference.
It seems like either one could work much the same way in terms of ease of distribution, but I agree UBI sounds simpler and more direct. Maybe just because it's something new and it's straightforward in principle so we can fantasize about it actually working efficiently.
I imagine UBI as a system where every citizen gets a monthly check, no questions asked. It shows up in the mail or gets direct deposited and that's it. And if someone can't receive it that way, say if they're homeless or don't have a bank account, maybe there could even be a place they can show up and collect their money in person. This might still be a pipe dream but it doesn't seem impossible, the hard part is actually figuring out how to pay for a UBI program.
Contrast that to sticking it into the existing income tax system. I imagine that would mean you'd only collect the money annually, and only if you file a tax return. Lots of people without much income don't file tax returns so that's already a blocker. And once the money is gone, a year is a long time to wait for another payment. Of course there's no reason a negative income tax couldn't still be distributed monthly and made more easily acceptable, but there's just a lot of baggage around the thought of dealing with taxes.
I don't know if I would call that a significant difference, especially since neither one of them is really tied to any specific logistical approach. You could pay a UBI as net of withholding so that it comes once a year in the same check as your tax refund. You could pay a negative income tax on a weekly basis so that net recipients get a tax refund check every week.
For UBI, you need to / get to have a direct line to every person/citizen. For NI, they come to you.
I honestly have no idea which one is better/easier from this perspective, it just seems like the logistics implementation is another significant difference.