administrative overhead costs

The fundamental component of the Institute on Race and Political Economy's plan is expanding the EITC, or Earned Income Tax Credit, an already existent program. Implementing MTBI through the EITC doesn't increase costs anymore than a UBI would as the internal infrastructure already exists in the IRS. If you were to implement a UBI without the EITC, you'd either have to create an entirely new program through the Treasury Department or otherwise, and be able to find every person in the US to pay them with cash or cheque. That doesn't sound like more administrative overhead? Maybe I'm biased because I particularly like the idea of an MTBI but just the implementation of a UBI sounds more of a practical nightmare than MT.

any stigma from receiving it

Cremer & Roeder, '15 suggest that a means tested system will have comparable stigma to other existing programs such as SNAP, which is high, but in the US political climate, there will be more support for a means tested system, and "political economy considerations do not appear to justify a universal system." Although there is still a stigma associated, the net benefit of having political backing that's miles ahead of a UBI makes it a much more realistic plan to pass in current day.

flawed at the foundation

I have given examples in other comments showing that MT works, mainly the Stockton trial, but I'm more than happy to provide empirical studies from other countries implementing MT on a larger scale.