I have a HQ16 bought off Craigslist, plus a pcquilter, which is a robot that moves the HQ16 on the frame tracks. It works via a computer. I've never been sorry to have purchased it. Most problems I have had with my set up are due to operator error. I can sew up to a 12" deep pattern, but only on smaller quilts. Most lap quilts I quilt at 11", bigger quilts require a pattern that is 10" or less because of the bulk that accumulates in the harp as you quilt.
Have fun with the shopping and with the long arm.