How reflective is POPVOX?
POPVOX appears to rely on people volunteering to voice their concerns. So I dont know about the general applicability.
People who are politically active or opinionated, especially conservatives will always weigh in on such issues as FairTax.
The bottomline is that a large swath of the public still needs to hear about the FairTax and what it is exactly and they must also be coached against the specious arguments of its detractors.
A good indicator of FairTax progress is the average number of daily signups to memberships in the AFFT, the grassroots org for the FairTax. Last I heard it was about 800 people per day, every day. But thats only about 300,000 people per year which is inadequate.
The good news is that new registrants to AFFT stick with it, once a FairTax supporter, always such; once one gets it, never can seriously consider any other alternative.
Another useful statistic for activists is that it takes about 3000 activists in a US Congressional District to turn the Rep to the FairTax.
Where POPVOX stands in all this I dont know
Self-selected samples are full of those who feel strongly one way or the other. Obviously not representative samples.