I have the original HQ16. It can be used on a sit down table or on a frame. When I purchased it, 2nd hand, I had no idea what I was doing and went through the usual trial and error. while learning. Other than operator error, I have had no problems with it.
It is on an 8 foot frame - 96", but I wouldn't do more than a 90" quilt on it, and that might be a bit of a stretch.
MY HQ also has a pcquilter - robotic, computerized quilting. It works very well. However, I only do end to end patterns. The pcquilter runs with an old XP pc which is nearing the end of it's useful life. When it goes, I will upgrade everything. Haven't decided what to...yet.
The HQ throat is 16", but on the frame only about 12" is useful for quilting. It works well for me, but I would really love more throat space.
DH has maintained it for me since it was purchased it used in 2010. All that it has ever needed maintenance-wise was cleaning in the needle area, but of course, he opens it all up and cleans and inspects.
I suspect the Sweet 16 could have been used on a frame with a few modifications.