I have a Designer SE and also a Sapphire 870. I don't think I could live without the needle threaders! They work great. If you find that yours doesn't work well, it could just be an adjustment problem. When you take your machine for it's service, ask the technician to adjust your needle threader too. When my husband worked on machines, he always adjusted the needle threader as part of his service. I am pretty lucky--he works on mine if it ever gets out of line.
Also, about the thread cutter--I love that feature too! I did find that with some threads, it would cut too short and unthread the needle. It was usually cheap thread I was using and once I changed to better thread, the problem was solved!