I have both. I love them equally but for different reasons. I use them equally to work in Z2. However, I feel the Assault Bike gives me better anaerobic work when I choose to do it. I am not a climber (I am a peakbagger) so I can’t speak on how it will supplement rock climbing. I will say this though, when I’m done working with the SkiErg, I feel similar to the way I do when I get out of the pool after having done some laps. If i HAD to pick one, I would go with the SkiErg. It’s so unique. You can go for a run or hike then hop on the SkiErg. Hope that helps.