I've been looking at adding to the home gym, with one item being a ski erg. The focus is on cardio right now. I've got a c2 rower that my wife and I love, but wondering if something like an air bike is more practical (compared to the skierg). I do CrossFit, and she runs halfs and marathons and does some CrossFit to humor me. We have access to everything but a ski erg at our local gym (YMCA that has its own facility for CrossFit/swimming/old men walking around naked in the locker room).
Waste of money/gimmick or worth looking into?

Love the ski a ton

We have one at the CrossFit gym I work out at and it is a pretty good cardio workout. Depending on how you use your lower body you can focus on a few different muscle groups with it. It is definitely a cardio machine, more than a rower even.

I have a SkiErg and and an Assault Bike at home. I wish we had gone with the rower instead of the SkiErg, so in my opinion, since you already have a rower, I'd go with a bike. Maybe a BikeErg or Assault Bike.

The ass bike kills my cardio a LOT more than the ski erg. I don't really like the ski erg.

If you were in South Carolina, maybe we could work out a deal.