They are great units, and yes, very similar production boost as nailers. I feel the same way about my nail guns. But, like any tools, there is always the "ooh, what if it had/did this..." factor, which is what drives us (painters) to own a whole fleet of sprayers.
For us, the SprayStation bridges a critical gap between our cordless sprayers and our more esoteric hvlp units that we save for the super fine finish stuff. We will take the SprayStation out and run exterior stain through it on a spindle rail system for instance, wouldnt do that with our nicer rigs. But that is whats impressive about it, its a tough little rig that puts out a nice finish reliably.
And you are right, the man hour savings versus any manual application method probably gives the whole Earlex line as high of an ROI as any hvlp's out there.