It's better for income earners, but it's much worse for people who've saved money for retirement, who paid taxes up to 50% on their income in the first place and now have to get it taxed yet again.
The NRST will not simply replace the income tax. That will be the promise, of course, after an initial period of parallel operation, also of course. In fact, politicians will almost certainly just end up charging us higher taxes. The income tax is too important a mechanism for control to be given up.
The real purpose of the NRST is to keep our nearly bankrupt government rolling - now by raiding the savings of the elderly.
You are right-that is the one and only big disadvantage. I would support a phase in of the NRST beside a phase out of the income tax but ONLY if a constitutional amendment was passed that said that after the year that was the last year of the phase-out that the income tax would be unlawful.