I have an Hq16 that I bought used in 2010. It works extremely well and has given me no trouble whatsoever. (There have been several incidents of operator (me) error, though!) I highly recommend the HQ line of quilting machines. If I replace what I have, I will probably get another HQ.
My hq16 is on a frame and runs via a computerized carriage, the pcqullter, so I don't need the Stitch regulator. However, if you will be quilting on a table, it might be useful. My understanding is that it keeps the stitch length consistent while you quilt. I have never used a stitch regulator, so others may be able to provide you more info.