The titles of the articles Imax and A99 Exposed, referred to in this thread, probably suggests something negative to most readers. Instead, I think the author likely meant that the antennas being exposed; were just opened up to view inside.
Can you really argue that these antennas were not a real boon to communications in the CB world at a time when safety and effectiveness were at issue? Arguably, the A99 probably still prevails as the most widely used CB antenna in the world, bar none and is also very effective at doing what it is supposed to do.
IMO, the issue about the ground plane kit is often miss-stated as well. In a technical sense the GPK, if effectively installed, could possibly provide some modestly improved results. It is true, as ‘Doc notes, that neither really needs the GPK in order to work, but so will a bucket or a hose with a few holes in it work. The issue is how much better will the improvement be if these antennas were correctly and technically modified and then measured and compared on an actual test range? Even doing this, however, does not consider the varied locations for the general user, just another issue that plays into how and why.
Also, the comment that the Imax is better built is not proven out by the many testimonies that I have seen on these Internet sites.