i have one and i like it very much. it's like a gun that shoots a plastic thread with tags on both ends. the first tag folds back so it can go through your fabric, along with the plastic thread, and the second, larger tag, stops everything from passing right through. it creates a very flexible line of plastic that holds your quilt sandwich together much the same way as pins, but it bends with the fabric and is less lumpy. before my longarm, i used it quite a lot. now i use it to attach my quilt backing to the leaders of my longarm, then the batting and top to the backing. much faster than pins and you don't get stuck. i go through and then come back up.
when i used mine a lot, i used the plastic grid that you can buy for it. it made it very easy to use on the table top.