Welfare politics are driven by resentment, and offense that "My tax dollars are paying for lazy welfare queens to drive Cadillacs!" Because of this, there's a tremendous amount of overhead built into fraud prevention and making sure no one who isn't utterly desperate gets it.
With GMI, there's no justification for class resentment - you get the same benefit as everyone else.
Guaranteed Minimum Income is the idea that if your own income is insufficient, the state will step in and provide one for you. The conditionality in that definition, however, means that it would be a means-tested programme with all the attendant implications for marginal tax rates, poverty traps, class resentment, etc.
A Universal/Unconditional Basic Income is different -- it's provided to everyone with no means testing whatsoever. I think that's what you meant, based on how you're using it. But just be aware that GMI/UBI are actually quite different things.
With GMI, there's no justification for class resentment - you get the same benefit as everyone else.