I have a sweet 16 and I am really happy with it. I prefer the sit down to a long arm and really didn't want to give up the space that a long arm would need.
I am slow at making quilts and only use it on my quilts so not a lot. My DIL also uses it occasionally. She sat down, I gave her a few tips and she stitched away on a quilt and did a beautiful job. I took quite awhile to be able to make anything that looked nice.
I got the stitch control and never use it. I use the ruler foot. the open toe, the echo feet and the couching foot often.
I have been working away on my machine without the tension kit, I didn't even know that it was out there. It is something that I always thought they should add to the machines and now that I know about it I will be looking into it. It would be a great help to you when you are new to the machine.
I love to use different weights of threads and change colours and weights often within the quilt. I enjoy doing free motion and ruler work and I know that my quilting is not precise but I am very comfortable with that.
I am presently working on a king sized quilt and am just enjoying adding in different designs as I go. you could be generous and call it custom but I just call it playing around.
You will really appreciate the larger work space of the table extensions when you work on bed sized quilts. I have no problem with the quilt size. I work in a clear nest so there is never any pull.
The biggest problem most people have when they first get a quilting machine seems to be tension settings. Although the readout will help to give you a number to go to you will still need to get used to changing the tension and changing your bobbin tension for different weights of thread. I think that applies to long arm machines as well.
I hope you enjoy your test drive. There is a wealth of knowledge on this board and always someone willing to help you so I'm sure you will get more input.