I have the sweet 16 and I am so happy that I got it.
When I bought it I was sure that I needed the stitch regulator so I bought it as well. I used it when I first set the macine up and then decided to try stitching without it. I haven't used the stitch regulator since even for ruler work. I do find sometimes the larger rulers are difficult though and I might get it out again to see if it improves my consistency with them.
You can add the stitch regulator on later.