The choice for the surtax is perverse: a major point of having a UBI as opposed to means-tested social benefit program is to maintain the marginal benefit of additional income; having a "surtax" that reduces the benefit progressively with income that kicks in at a fairly low income level and proceeds to increase up to a level that's still not a high income is a fairly horrible idea that defeats key elements of the basic idea of a UBI.

I'm not a fan of radical big-bang all-at-once UBI replacing other programs swap anyway (favoring a UBI tied to a dedicated revenue stream that displaces means-tested benefit programs as it ramps up, instead) but even among big-bang implementations this is particularly poorly designed.

(1) The "surtax", as discussed above.

(2) Because it relies on electronic deposit to a bank account, it relies on (but does not provide) a solution to the problem of the unbanked.

(3) The decision to apply it only to adults is dubious, but if you are going to have an age-qualified UBI, it should apply at a minimum to all legal adults -- everyone over 18.

(4) The benefit (after deducting the required health insurance purchase, which for those with no other income simply replaces Medicaid, which is eliminated [0]) is below poverty level. Which would make sense as an initial condition of a UBI which was built to grow over time, but this proposal doesn't appear to be -- its a proposal, therefore, to maintain, rather than alleviate, poverty.

(5) Apparently, the author prefers to fund the UBI for everyone largely by continuing the existing regressive, labor-pays-only, payroll taxes (Medicare is flat, Social Security is flat up to a limit, and then capped, making it -- and overall payroll taxes -- regressive overall), whose current regressive structure (including the flat structure of Medicare) is justified based on the idea that they are buy-ins to benefit programs that provide consistent (Medicare) or capped, contribution-determined (Social Security) benefits. Aside from there being no sane rationale that would justify this, it entirely eliminates UBI's utility as a system to help adapt the economy to deal with progressive automation and the dynamics of the labor market moving toward a larger pool of jobs that have lower returns and a narrowing highly (and increasingly-highly) paid pool of elite workers. Moral issues aside, payroll tax structure can't support the author's proposed UBI going forward.

Then again, I suspect that's the author's intent: kill Social Security, Medicare, Medicaid, etc., and replace them with something that cannot function in the long term. After all, this is a proposal for a social transfer program from an author who has written an entire book setting out supposedly universal laws that each individually (and, a fortiori, all combined) supposedly justify the conclusion that all social transfers are inherenty harmful and should be eliminated.

[0] The author indicates the healthcare component is too complex to discuss in the article, but this is also a particularly worrying component. Looking at what $3,000 gets you on the health insurance market, this mandatory insurance purchase replacing Medicaid might make the poorest of the poor significantly worse off by itself.