How accurate is the new appraisal system?

Solution 1:

The new appraisal system shows the exact IV's of your Pokemon:
each chunk represents 5 IV's. If the bar is empty, it's 0 IV, if it's full and a darker red colour, it's 15.

I don't use the Pokegenie app but I assume it's just looking at how full the bar is and telling you the exact IV as it can be a little tricky to tell at first just by eyeballing it.

For example, it's obvious when it's 10 or 15 IV's, as the bar's filled up right to the end of a chunk; but when it's 11 or 12 it might be a little hard to tell the difference at first. But after a little practice, I personally don't think an app is necessary to tell you what IV's your Pokemon has anymore.