I too have the designer SE. Great embroidery and sewing machine. However I have taken multiple free motion quilting classes and have practised alot-still am not happy with doing fmqing on it. Your financial situation will probably be what determines your choice. I am cleaning up an old Singer 301 and going to practise fmq-ing on it. That should let me know if it's me or the Designer SE that is the issue with my fmq.
Kat