Has anyone heard of this so-called quilting frame that works with your machine? Does it actually work? Pros and Cons? I saw it on Craigs List, but the info is very vague.

It's a real thing. Kind of a cross between a Flynn frame and a stand up machine quilting frame.

http://www.easyquilter.com/

Is it worth $100? I cannot envision that my machine would keep threaded throughout. I have a Viking D1 & a Quantum Singer.

We all have to change the bobbin no matter what size frame you have. I would think it's probably worth the $100 to get your feet wet but if you are truly wanting to quilt on a frame, you will outgrow your machines and this frame quickly. If you just do small quilts and have a real problem with storage space, this might be just the thing for you. It's like a mini-version of a table-top machine quilting frame. They have upgraded to a different track system which can be purchased & retro-fitted to this model for an additional $199 to $250 plus shipping (I found both prices so I'm not sure which is correct). I don't think I would upgrade it however. If I decided I really liked frame quilting, I'd save my pennies for a larger machine & frame.