Yes I have extensive experience with the Ski Erg by Concept 2. For those who don’t know about this here is a brief explanation. The Ski Erg works on the same principle as the Concept 2 rowers with are fairly ubiquitous in the fitness world as being an important piece of training equipment in the rower’s arsenal. Concept 2 developed the Ski Erg for Cross Country skiers to use for training the double pole technique. The newer Ski Ergs also have the added functionality of allowing the arms to be worked in the diagonal stride technique (swinging arms opposite from one another and the same leg; as in running).
Because of my background in training XC skiers I bought one of the first Ski Ergs when the became available and have recently bought one of the newer versions. I and my skiers have spent hundreds of hours using them over the years. Like the C2 rowing machines they are well made and very robust. They have a fairly good transfer over to XC skiing and skiers use them in some very specific training methods and not for general conditioning work.
For general fitness I can see how they would be a good addition to many commercial gyms. However as a climbing specific training tool I can’t see how they would be especially useful.
Climbers who use my gym use my C2 as a way to warm up for getting on the small bouldering wall. But I can’t see its transfer over to climbing as anything other than very general conditioning. For instance: As part of the general muscular endurance circuit or as a warm up tool.
I hope this helps.