I have had little trouble priming on my Co-Ax, but I'm pretty mechanically inclined (life long machinist/mechanic). Maybe some have trouble adjusting the shell holder jaws on top of the press or maybe some think it's too slow, but I used a ram prime for many years and my Co-Ax ain't slow for priming (and some reloaders are challenged by correct hammer use). The adjustments for the jaws are really simple, straight forward, just takes a bit more care than sliding a shell holder in a ram...
Precision reloading and past "experienced" loaders tell of the presses' potential, not much about who pulls the handle. The case "self centers" in a "floating die" so there is much less possibility of getting misaligned bullet seating and case sizing. All these things just point out how good a Co-Ax is and is not a comparison to any other press. If there were other presses built on the same style/principle as a Co-AX then a comparison would be appropriate, but there ain't none.
The adapter sold is just, in my opinion, for reloaders that cannot get the dynamics of a shell holder not like the "RCBS" universal style.
In my opinion, the Forster Co-Ax is a very well designed, well made press that is easy to use and has the potential to make precision handloads. Better than a single stage? In many ways, yes...