they sell these frames as combos with a machine- several models.
but yes you are limited to your design size
that being said alot of quilters do a very good job with these frames and domestic machines
if doing a larger quilt you will just need to remove it from the frame and reload( work from one end to the middle the reload quilting the other end to the middle)
but it can and is done
check yahoo groups there is a group for these frames and you can get alot of info there