I am sorry you are already having trouble with that Scala2 pump. They haven't been out very long, so I don't have a lot of experience, but I can see a lot of things that can go wrong with those pumps. To answer your question, no you can't use a CSV with a variable speed pump like that one. But the variable speed thing is not working, or it wouldn't be cycling like that. The speed is suppose to vary to KEEP it from cycling.
First question is, do you have a check valve in the suction line?
I don't know how the extra expansion tank will effect those pumps. But I have read that they have a little tank built inside the unit itself. I can see where an improper air charge in the internal tank could cause a problem, as it should help cushion the pressure transducer. My recommendation is to check the air charge in the internal tank. Then if the pump is still cycling on/off I would look at getting a warranty credit.
I don't expect those pumps to last very long, but they should at least work when new out of the box. A good jet pump with a regular pressure switch and pressure tank would last 30 years, and adding a Cycle Stop Valve to it would stop the cycling and give you the strong constant pressure like the Scala2 pump is suppose to be doing but is not.