The 820 and 830 can be put on the Bernina frame to quilt with. They only give you about a 8 inch quilting distance? They do a nice job for the limited space available especially if you have the computerized system with it. If all you want to do is quilt a design across the quilt at intervals you will be happy. If you want to quilt bigger design over a larger area, I would think you would need a mid arm or long arm machine.
I think you need to try the set ups before buying. See if there are dealers of the Bernina set ups and true long arm machines in your area and compare them. This is just my opinion so the decision is up to you.