I also think some of it has to do with your machine. I have a Singer that comes unthreaded all the time when I use the thread cutter but the auto threader works wonderfully. My Juki does a marvelous job cutting the thread but I never could get the needle threader to work 2 times in a row without trouble :p

I don't use the cutter on my machine.

when you say "nests" do you mean blobs of thread that clog the machine?
or do you mean it makes a bit of a blob on the back side of the piece at the beginning of the seam?
mine does that, too.
it used to drive me crazy because it doesn't look neat and tidy.
then i realized that it does keep the seam from coming apart at that end.
once the piece is done, that odd little knot doesn't show or create any problems as construction proceeds.
sooooo ... i'm training myself to ignore it. :)

I use a little piece of starte/stoppee fabric most all the time, this takes care of any bird nest of thread on the next sewn fabric piece. But if I don't, I don't worry about it, my thread rarely comes unthreaded, the thread cutter is a time and hand saver, less arm movement. For those that have knee lifts and don't use them, they are also a time saver and arm saver. Instead of using your right arm to lift the pressure foot, it can be doing something else while your knee lifts the pressure foot. Once it becomes a habit you'll wonder why you didn't use it before. THEN try using a machine without either of those features and you'll try & lift the pressure foot with your knee and it won't be there. We all have special features we love about our machines and are happy to pass them along.
Keep sewing:o

Ihave a 1500 too and had the "unthread problem. Thanks for passing on this hint for resolving. I love this machine for FMQ and will try the suggestied threading.

I have an auto cutter on two of my machines but don't use them. I don't get nests or such by not using it, but I don't like the knot it ties if I use the cutter. Guess it's a personal thing.

Sorry.. Double post.

The thread cutter saves me time because I'm not continually groping for my scissors and then putting them back. When multiplied out over the course of all the snipping on a larger quilt, you might save more than an hour! It also saves you thread because I can just start sewing again without having to pull the threads up. No nests, no unthreaded needles. Maybe some work better than others? It is one of my favorite new fangled sewing machine features.

I have one on my Bernina and I LOVE it. I have never had a problem with nesting or with the needle coming unthreaded.

I have a Juki and the thread cutter is great. I notice when the quilt top is finished there are no loose threads left in the seams. Some quilts I get from customers almost need a hair cut before I quilt them.