Hmmm…not a question I’ve ever heard before about roll up/roll down! I agree with Jill that roll up has a tendency to cause tension in neck muscles; but once a client understands the exercise, this shouldn’t be a huge issue. It absolutely does work the core muscles!
As for roll down (with the roll down bar on the Cadillac/Tower), this one’s a bit trickier. You really have to be “connected” to your core to get the full benefit. Think about pulling your abdominals back towards your spine as you roll down to accentuate the spinal articulation…and KEEP them pulled back/engaged as you roll back up. You’ll definitely feel your core working!