To me there is no comparison. I have the stitch regulator for my Bernina and we are getting a long arm to quilt with. There is so much more convenience and utility with a larger machine. You have much more control over the quilting process. It's much better to be moving the machine over the fabric than to be doing it the other way around. Rather than having to reposition my hands on the quilt to push it through the DSM. With a mid or long arm, I can see the whole picture laid out in front of me. I can concentrate on the actual quilting process, rather than having to push the quilt through and quilt at the same time.
You have a lot more options when quilting in a frame with a long arm. Even if you use a frame for your DSM, you still have a very limited quilting area usually 4 to 6 inches, with a 16" mid arm you can figure 10" quilting area and with a longarm you have up to 20 " or more depending on the machine, if your arms are long enough to access it all. You can use whole width pantographs with a table frame, which is sometime difficult to do with a frame for you DSM. You can use tools like rulers and a Circle Lord or Quilt-EZ stylus and templates with most mid arms and long arms. I don't know of any adapters for DSM to use those tools.